Buoyancy Ideas?

[pjl83]

I was speaking to an "old boy" at work the other day about bits and pieces to do with boats. He has built and fitted out many boats down the years. He's a great guy, always willing to help and full of good ideas. When I told him that my sole wasn't down yet, he told me of an old bouyancy aid that he has used in all his boats. Where you have the depth in the bilge and before the sole goes down, fill it up with 2litre plastic drinks bottles, uncrushed and with the lids srewed on.

It sounds a little bit silly, but as he says - they are light, they are extremely bouyant and cheap! If the worse thing ever happened and you were taking on water, imagine the vital extra bouyancy that a few dozen plastic bottles would give you. I've got the whole family now saving up their empty bottles ;)

What's your thoughts guys and gals?????

[Mike]

Of course, I am not qualified in the area of design, let alone on buoyancy. However, I truly believe that it is vitally important to ensure your boat can become a liferaft should the worst ever happen.

In this respect, you will find that most designers these days ensure you have areas of buoyancy built in to the design. Most seem to go for under seat buoyancy, particularly in small dinghies, JohnW's Tender Behind being no exception.

I'm not too sure I would want my buoyancy to be below the sole, simply because it seems to me it will inevitably cause the boat to turn turtle, which would perhaps leave you sitting on the bottom of the hull rather than in a swamped hull. I note some designs have buoyancy chambers in the sides, below decks, and others simply have watertight bulkheads.

This is perhaps a question for the designers or naval architects to answer. My own view would be that it's better to have some buoyancy somewhere, even if underfoot and of plastic bottles, than none at all. Otherwise, that Sea Sled could quickly become a Submarine Sled, Paul. So, why not?

An alternative would be to enclose the areas below any seating, leaving a seal-able inspection hatch in place to allow access and inspection where needed.

One bit of good advice I have from JohnW is to avoid using polystyrene foam if you can. Many fill their buoyancy areas with that stuff and it can, in fact, hold water and cause plywood to rot. Air is not likely to do that provided you can change it by opening the ports and ensuring it stays dry inside.

Interesting idea and very inexpensive, though. When kayaking in the Sixties, I used to stuff a big plastic vinegar bag into the bow and stern of my PBKs to provide positive buoyancy in the event of holing the hull. That worked very well in keeping the hull afloat and upright. You could, in fact, still paddle the thing ashore if it was fully swamped.

Regards

[bowdidgemarinedesigns]

Of course, I am not qualified in the area of design, let alone on buoyancy. avoid using polystyrene foam if you can. Many fill their buoyancy areas with that stuff and it can, in fact, hold water and cause plywood to rot. Air is not likely to do that provided you can change it by opening the ports and ensuring it stays dry inside.
Regards

Mike, I hear so many people commenting on not enclosing high density foam in enclosed areas (ie seats etc)as it will cause rot in plywood, its unbelievable. If you contruct it from plywood, you need to encapsulate the plywood in epoxy resin (minimum 3 coats) and treat or think of the compartment as a water tank. Water tanks don't leak so construct the bouyancy compartment as such and you WILL HAVE NO PROBLEMS. I've constructed boats using the above technique and on doing modifications 15 years later, the bouyancy compartment and foam within was in PERFECT condition. If high Density foam is not used, but only wanting an "air" tank, the tank itself must be seperate from the hull of the boat and not used as a "wall" for the compartment.

Coke Bottles: Don't even think about it. Under the ABYC regulations/ Australian & Canadian Builders Plate and RCD, it is not allowed. Using such and you do at your own peril. If an accident causing grevious bodily harm or death and on the courts finding, coke bottles and such are found, you will be held liable and charged. This is serious stuff we're talking about here and not something to be taken lightly

regards
Mark Bowdidge (MRINA)

[Mike]

Just what the doctor ordered: some more expert advice on this subject.

It seemed to me a bit 'Mickey Mouse' to use plastic bottles below the sole for buoyancy. We don't comply with ABYC rules here of course but with the RCD. And a home build does not have to comply with the RCD unless you choose to go that route.

What Mark is addressing here is the commercial aspect of boatbuilding in that a manufacturer MUST comply with the rules applicable or face the music when things go seriously wrong.

My own advice would be that the standards imposed on manufacturers are mostly for good reasons of safety and should give the amateur something to consider in all he/she does.

I would humbly suggest that a boat designed by a reputable designer is very likely to be safe and sound. If you intend to deviate from the design in any way, you should always consult the designer for advice before deviating in any significant way.

Thank you, Mark, for reminding us all of the safety aspects in boatbuilding.

As to the use of foam in buoyancy compartments, the RCD does not advocate its use or prohibit it. It simply requires buoyancy tests and inspection by a qualified surveyor. One aspect of its use here in the UK is cost. This two part expanding foam stuff is darned expensive here - as is just about everything when compared with anywhere else in the world, including elsewhere within the EU, strangely enough.

I have never used the stuff myself, so I cannot comment on whether it causes rot or not. However, if JohnW don't like it, then I am certainly not going to ignore that. I think your own advice on how to properly use it sounds perfectly plausible but, again, there is a huge cost issue here in making 'water tank' compartments of every buoyancy area and then filling with this expensive foam stuff.

Methinks you Aussies get a much better deal on most things than we do. Our petrol and diesel prices (currently at about £1.10 per litre!) are more than double what you guys pay, despite the fact that we are an oil exporting nation. Much the same applies to just about everything else we buy. When it comes to anything with 'marine' stamped on it, the rip off becomes even greater in much the same way that the 'aviation grade' stamp does.

We live in 'Rip Off Britain', believe me, and we can't do much about it for the time being. We peasants will eventually have our day, I feel sure, but it will be some time coming. In the meantime, we have to watch the pennies.

Kind regards

[bowdidgemarinedesigns]

What Mark is addressing here is the commercial aspect of boatbuilding in that a manufacturer MUST comply with the rules applicable or face the music when things go seriously wrong.

Actually Mike, it applies to amatuers as well. No one is excempt. The Australian builders plate standard is the same standard used in Canada (Canada Transport ) which is based on the ABYC standard. (Although in the USA it is not legislation or mandatory for amatuer builders to adhere to.

Here in Australia, without it, you cannot get your boat registered. Now this standard, at this stage, is only applicable to power boats. Although, at the last Naval Architect meeting, the Australian Maritime safety Authority informed us that there is a world wide push for a one standard that "ALL" boats will need to apply and meet. It's in the beginning stages, but probably won't be here for another 7-10 years.

As I said previously, if you choose not to abide, even though you may not be required to, you can leave yourself open to litigation and in this present world and attitides, it's a real possibliiity. Also, if there is an accident, you can also be charged. It's already happened here in Oz on a number of occasions already.

Your decision and choice.

Mark

[Mike]

Actually Mike, it applies to amatuers as well. No one is excempt.Well, Mark, it may well apply to amateurs in Oz. You would know more about that than I do. However, the exemptions available in the EU RCD include one that applies to any home built boat between 2.5 and 24 metres LOA. Essentially, it means you can build however you wish at home and, provided you make no attempt to sell the boat on to others within the EU for five years after first use, there is absolutely no RCD compliance necessary. And registration of your boat is another matter altogether and does not require RCD compliance either.

I don't doubt that there is a push by manufacturers to have the standards of which you speak apply across the board. It is, after all, entirely in their commercial interest. However, I for one would resist any attempt to prevent the amateur boat builder from building his dreams if it forces him/her to comply with obscure and inaccessible standards that cost an arm and a leg for him to comply with, especially on a one-off build. To comply with the RCD here would cost me several thousand pounds for just one boat and would not help others in that each build would differ from mine (there is no way at present to permit a naval architect to certify his type for the home builder to comply with).

As I said previously, if you choose not to abide, even though you may not be required to, you can leave yourself open to litigation and in this present world and attitides, it's a real possibliiity. Also, if there is an accident, you can also be charged. It's already happened here in Oz on a number of occasions already.
Again, an interesting view but not quite right, Mark, in that a home builder is building for him/herself - or he/she is a manufacturer and MUST comply with the RCD.

Litigation against oneself is unlikely, though it is entirely possible that a passenger aboard may sue a home builder just as you say. It would be a weak defence to argue that no RCD compliance was necessary but negligence (or gross stupidity) would not be a defence at all, of course. It would be necessary to prove that you took all reasonable steps to ensure that any and all foreseeable events were considered in the method of construction and its build, which is why it is wise to co-operate closely with the designer and not deviate from his design without his okay.

In this litigious world, nobody can be certain of being in a defensible situation, including manufacturers who certify their compliance with the RCD. It may be that they have not. Or it may be that they think they have but have not. Or it may simply be that an employee did something outside the scope of his/her employers' instructions that rendered the boat non-compliant.

The real problem here is the obvious one in that the problem with legislation that seeks to protect individual rights is that it invariably encroaches upon the rights of a much wider group of individuals.

Here in the UK, there is a very long history of amateur boatbuilding. And it has to be said that some amateurs can and do build boats better than some professionals do. It is not, in my view, necessary to impose unfair and costly standards upon people who are building a boat for their own intended use. And the home build exemption available under the RCD clearly respects that view in allowing the relevant exemption.

I will build my boat and be happy to use it for five years before selling it on to someone else. After all, if she serves us well for that time, I feel she will have proven herself safe and seaworthy. If not, then neither I nor my boat is likely to be around. Thus, the boat would not be able to cause death or injury (except perhaps to divers who enter the wreck at their own peril) and I won't be around to be sued by anyone. Q.E.D.

One final point is that it is not that long since most boats (as opposed to ships) were home built and built for the exclusive use of the builder. And many designs still in use today are very closely related to those designs that proved themselves safe and seaworthy over very many years of use. I can think of many examples of this and it has to be said that the spirit of adventure and courage is not lost in us all. Many of us wish to sail a boat we have built with our own hands and we surely ought not to be required by any legislature to build and behave as if we are professionals. There must be room for the inventive and dedicated amateur to thrive and to use his/her boat for his/her own pleasure. Just as he ought to be permitted to drink and smoke while sailing her and to do what he wishes provided he/she does not hurt or impose his/her will upon anyone other than him/herself. Don't you think?

Best wishes

[George Waite]

Mike/Mark
Aside from all the legal/regulatory/state interference stuff the most dangerous aspect of loose bouancy items in an enclosed space is that they can break loose and actually trap/drown you.
George

[pjl83]

If the boat already has bouyancy built into the hull then surely a little "free" bouyancy under the sole won't hurt anything. How can it cause any harm if it's trapped in the space between the sole and the hull. The sole is fixed down and glassed around the edges so there's is no physical way that the bottles can come away from the boat. For them to become seperated from the boat, the very fact that I'd used plastic bottles would be way down on my list of problems.

I understand the legal stuff regarding doing things properly and with safety in mind it's a fair call, but in addition to what's bult in I don't see why it would be an issue?

[George Waite]

PJ
I did not ralise that the bottles were to be glassed in. If this is the case then why not make the space watertight and dispense with the bottles?
George

[pjl83]

Purely for ease of build and cost George to be completely honest. The space I'm talking about is where the bung is fitted and will also house the bilge pump. As the boat is being designed with fishing in mind, there will be a "deck wash" pump fitted for cleaning down the deck, and the sole will be layed so it slopes towards the aft of the boat where there will be a drain leading to where the bilge pump sits.

[Mike]

Aside from all the legal/regulatory/state interference stuff the most dangerous aspect of loose buoyancy items in an enclosed space is that they can break loose and actually trap/drown you.An excellent point, George, and another argument in support of using watertight compartments for buoyancy rather than high density foam fillers. Air is not likely to trap or drown you and can provice a source of breathable air to facilitate an escape from a sinking hull.

If one considers a sinking following a collision of some kind, I can imagine even loose, or loosened, foam buoyancy could become an entrapment hazard. Again, a watertight air chamber when holed will fill with water - but only in the area of the impact.

On the plastic bottles issue, I somehow have a feeling that buoyancy built into the bottom of the boat is likely to turn the hull over as it sinks. I say that presuming the boat has no built in buoyancy elsewhere and cannot yet see any such areas in Paul's Sea Sled hull. Of course that raises the question of whether the design actually had any buoyancy at all when it was first built. I don't know the answer to that one.

If this was my build, I think I would be installing a seating arrangement that had watertight buoyancy/storage compartments beneath the seating. This, in an attempt to raise the centre of buoyancy. Having said that, I repeat that I am totally ignorant in the area of design for buoyancy.

It's an interesting topic, nonetheless, and I am enjoying the input from all contributors. A worthwhile thread, in my view. And an important safety issue.

Paul, with regard to your deck washing plan, and bearing in mind the debris that can accumulate from hauling in and cleaning fish, I would suggest you take precautions against the bilge pump becoming blocked. Even small fish scales can conglomerate and block a small bilge pump. An overboard drain would seem preferable to me - and quite a large one with a non-return valve perhaps. Check out these sea scuppers (http://www.seamarknunn.com/cgi-bin/ss000001.pl?page=search&SS=sea+scupper&PR=-1&TB=A&search.x=13&search.y=7) available in the UK at moderate cost. You could fit a pair of these on your transom above the cockpit sole. This could be in addition to the 'bung' you are installing at bilge level and leave your bilge pump free to empty water only from the bilges.

Regards

[Mike]

I did not realise that the bottles were to be glassed in. If this is the case then why not make the space watertight and dispense with the bottles?
GeorgeA good point also. However, is it actually wise to 'glass in' a cockpit sole? How then, does one gain access to the bilges? I suppose the answer has to be through watertight inspection hatches in the sole above the bilges. And, if that is the case, loose plastic bottles in the bilge area are very likely to get loose in the event of a disastrous occurence, surely?

And would it not be the case that a watertight, sealed, bilge compartment is a rare and untried thing? I certainly have not come across such a design before.

I am starting to feel somewhat confused by all this, to be honest. :grandpa:

[bowdidgemarinedesigns]

PJl83,
In small boats, I'm not an advocate of having bouyancy or sealed compartments under the sole. It has nothing to do with safety, but really has to do with the reality of boating when it comes to cleaning, washing out etc and also pressure. None of our smaller designs have buoyancy under the sole, it's all under the seats (the outer part or edges). Imagine a seat divided into three, the outer sections are the buoyancy compartments and the inner is simply for storage. We actually have a large PVC pipe glassed onto the hull (thru the seat section) That way when one is washing out the boat, it doesn't collect in the middle storage comparments but flows through to the back of the boat where it drains out thru the bung. The other thing to consider with sealed air compartments is on a hot day the air within the chamber heats and expands which can cause buckling or fractures with the air chamber. Buoyancy compartments filled with high density foam DO NOT experience this problem.
On the small boat designs that actually have sealed soles in place, not only do they have large inspection hatches but also incorporate limber and lighting holes for "breathability".

On the issue of using coke bottles, I was reading somewhere (can't remember) that a fella decided to use ping pong balls in conjuction with foam. His comments later were that if he could do it again, he'd dispense with the balls and just go foam. Too easy and in reality, far cheaper and effective.

[Mike]

On the small boat designs that actually have sealed soles in place, not only do they have large inspection hatches but also incorporate limber and lighting holes for "breathability".In which case, surely, the seal is not airtight or even watertight.

I imagine the object of such design is similar to the so-called sealed hatch designs in that the intention is to ensure that water ingress into the area is slowed to seepage rather than a flood, which allows you time to right the boat if possible and then get her bailed out - well before the buoyancy areas become flooded.

At least, that has been my own experience in the smaller cats. For example, capsizing a cat (a frequent occurence when racing) usually results in some water ingress into the hulls, despite the fact they are said to be sealed and watertight. Once ashore and the bungs pulled, they invariably had a pint or two of water inside the hulls. Water has this unique way of finding somewhere to get through despite our best intentions in design and building.

Mark's point about expansion and contraction of air with change in temperature is well made. And it occurs to me that much the same thing could easily happen with sealed plastic bottles. Once a few have burst in that way, the effectiveness of them as buoyancy would inevitably be severely reduced if not entirely negated with time.

I will stick to air buoyancy, I think. Given the massive temperature ranges in places like Oz, I could entertain the idea of using foam instead. Here in Blighty, I can think of only a few days in any year that could possibly present an air expansion problem so severe that it is likely to buckle or fracture the compartment. In any event, and as stated above, it seems unlikely that any air chamber is completely sealed to the extent that there wouldn't be a release of any pressure build up through, for example, an inspection port.

As an ex flier, it occurs to me that the use of pressure relief valves would overcome such problems. However, I have not yet heard of any such thing being necessary for the buoyancy compartments on small boats.

Just my rather ignorant six penneth, of course. :)

Regards

[pjl83]

I've been down to the boat this morning after reading through all these posts and thinking more and more about the issue of bouyancy.

Looking at the shape of the hull in the forward section, I think the hull may already have bouyancy built in. The shapes dont quite match and using a rough method of measurement, it seems that there is at least 6 to 10 inches difference in the internal height and the external height (measured from the tarmac below the boat).

568 567

It's difficult to see from the pic but I'm sure that sections of the hull circled above are indeed sealed pockets of air. Maybe those of you with more technical knowledge than myself could hazard a guess as to wether or not this is would be something that a designer would do? If not then I will think again about building something into the seating and storage areas. :bur2:

Thanks for all the input. It's good to hear ideas, and of course - reactions to my own ideas (good or bad). Sometimes when working alone you go off in your own thinking bubble and don't always step back enough to realise obvious things that you may be missing. :Christo_pull_hair:

[pjl83]

Check out these sea scuppers (http://www.seamarknunn.com/cgi-bin/ss000001.pl?page=search&SS=sea+scupper&PR=-1&TB=A&search.x=13&search.y=7) available in the UK at moderate cost.

I can't seem to see anything on this link Mike, sounds interesting though? ???

[Mike]

The link works for me, Paul. However, I returned to the site and have copied two pages that you will find helpful. Here they are below in PDF format.


569

570

I suggest you check around to see if the prices quoted at Seamark Nunn can be beaten but a couple of the smaller, 25mm, jobs fitted to your transom would do a good job for you, I think.

Best wishes

[Mike]

It's difficult to see from the pic but I'm sure that sections of the hull circled above are indeed sealed pockets of air. Maybe those of you with more technical knowledge than myself could hazard a guess as to wether or not this is would be something that a designer would do? If not then I will think again about building something into the seating and storage areas.Hazarding a guess, Paul, I would doubt that your hypothesis is correct. I would think that those areas are 'beefed up' as they are most likely to impact anything floating in the water. This design is intended to be fast, so my guess is that the designer opted for a thicker, much stronger, build in the bow and tunnels. I doubt they would contain air pockets.

[bowdidgemarinedesigns]

All I can say Mike is, my comments from the above and other parts of this forum is NOT based on theory, guesswork or from something read in some book or forum. It's based on our real life experiences of living aboard our 43 ft catamaran permanently, as our family home, for 11 years. During this time, we sail to 6 different countrys, cruising the pacific, and Indian oceans, where ocean pasages between countries ranged from 9 to 35 days as sea.
Once out there you have to take what is thrown at you, from dead calm to storm conditions with 60 kts across the deck, wind screaming through the rigging and all the while doing 15 kts and your doing everything in your power to slow the boat down as your bare poling. These types of conditions are exciting and yet at times, concerning. If we scale down these conditions and also the size of the boat, its all relevant. And what it all balls down to is SAFETY.
It wasn't till AFTER we came back ashore that I undertook my studies as a Nav Arch, and with these experience's behind me (over 36,000nm at sea) that we base our designs on.
For example, the Mushulu 12 design is based on our experences with yacht tenders an how it is reality , your worktruck. As a tender, it needs to have extra high freeboard and stability for carrying passengers, shopping, water runs. fuel runs. At times you'll go ashore only to find that when its time to go "home" the wind and waves are up and you have to pound your way back to the boat. You may have shopping on board or a jerry can or two filled with water. Its rough and your on a lee shore because the wind has swung, You clamber aboard, trying all the while to stop the dinghy from smacking into the parent boat. It's raining so you tie the painter and kick the dinghy out and awy from the boat. It's belting down rain and your srambling trying to get the shopping inside, checking the main anchor making sure your not dragging etc. Some time later, the wind dies down and you decide to pull the dinghy in and haul it up only to find its fill to the gunwhales with water and the only thing holding it up is the bouyancy tanks. Hope you have enough bouyancy here because now you have to climb in and bail it out and those tanks have to be large enough to support you, the boat , outboard and fuel tank without sinking or making bailing out impossible.
The point about all this is safety and the above is based on REAL life experiences and, you will get caught out. Question is.. are you properly prepared for it?

Mark

[Clip]

Sort of following this thread, and I do have one enquiry that is pertaining to the effects on bouyancy foam (single cell, marine type) from extreme cold? Kind of fitting considering the time of the year, and the weather you chaps are getting.

I wonder if the contraction of air voids in foam in a cyclic way, will eventually de-grade the properties of the foam. Since the foam is rigid, and only so strong it must have some effect on the longetivity of the product. After all my empty gas tanks collapse into tiny round balls of plastic in the winter here (down to -40C) if I don't leave the vents open.

I do worry about my new floatation chambers I have installed on the Whaler, and wondered that if the old damaged chambers I had previously removed, were deformed from the the expansion and contraction from temperature effects.

[George Waite]

PJ
Is it possible that part of your hull is of foam sandwich construction (the forward end) and of a thick lay-up of glass from say mid-ships onward toward the transom? I have seen this method of construction before and it only came to light when the boat was badly damaged. The foam had become sodden and the boat broke its back due to "slamming" under load.
George

[Mike]

Mark

As I have said, your points are well made. It is understood that you speak not only with the voice of hard won experience but with the knowledge required in your being a naval architect.

The point you do seem to overlook is that relatively few of our members are actually involved in building a live-aboard boat. On the whole, they would be relatively fair weather sailors of small boats. And none, as far as I know, is a professional boatbuilder. Thus, and as the title of these forums suggests, we are largely backyard boatbuilders, most of us based within the EU with some enthusiastic - and most welcome - contributors from elsewhere in this world.

You were, I understand, a professional boatbuilder and you are now a naval architect with considerable experience with design projects in the bigger stuff that the wealthy can afford.

Your Mushulu designs are great. I would be pleased to build one myself. However, and I make this point most humbly, they are extremely professional in their design specifications in that they are ply encapsulated in glass, they have built in buoyancy chambers that reduce storage facilities aboard, and they require, as I see it, a build to what is, or is very close to, a professional standard. This makes them more expensive, and a touch more difficult, to build than the average backyardie here looks for in a boat they want just to get out on the water and have fun.

I in no way criticize you for this. In fact, I admire your work in every respect. Your boats - all of them - are excellent, modern, designs. And I feel sure there will be people here in the EU who can and will build them. But many backyardies will perhaps shy away from them for two quite valid reasons: the cost of build and the higher degree of skill needed to do a good job of the boat.

Perhaps you will bear in mind the fact that the adventures you had while living aboard your cat and sailing just two of the Seven Seas are far removed from most people's aspiration. If conditions are bad, the vast majority of us backyardies would hope to be tucked up nice and comfortable in our beds at home and not battling the elements aboard a self-built cat or its tender.

In my own case, Jeannette and I turned away from a Blue Water design by Paul Fisher to a coastal cruiser designed with rivers and canals very firmly in mind as our main stomping ground. In putting to sea, we would remain coastal and, should weather become a threat to our safety, we would hope to be in port or close enough to sneak into shelter very quickly. We are assured that Rendezvous is capable of riding out most weather conditions, though she is far from being a blue water boat.

For the above reasons and more, the average backyardie over here is careful with the pennies and extremely modest with regard to their boatbuilding skills. Nonetheless, we have a proud history of building boats in the backyard which most of us are trying to uphold in what we do. And there are some among us who do a wonderful job of building the boat of their dreams. Indeed, some are perhaps more adept than the professionals may think we are. We look for a reliable and reputable designer to ensure the boat is capable of doing what we wish to achieve and we do our utmost to build according to the design.

As I said, your designs are unarguably sound and trustworthy. I would certainly build one myself. With time, I imagine there will be many sales for you in this part of the world. From my own point of view, I trust you can be patient enough to continue impressing us with the photos of your designs, the pics of builders of them, and your contribution by way of imparting your skills and knowledge for our edification. All these things contribute to your reputation here, whether or not this shows up immediately in your order book.

Best wishes

[bowdidgemarinedesigns]

This makes them more expensive, and a touch more difficult, to build than the average backyardie here looks for in a boat they want just to get out on the water and have fun.

Actually Mike, around 80% of our clients are first time boatbuilders are not one has spoken of building our designs being difficult. Quite the opposite, ringing us up commenting on how easy the whole boat just "snapped" together. They take on average 2 weeks to build ( around 2-3 hrs a day) which one can afford to do after work.

In regards to cost, its not at all expensive as one may think. The Mushulu 12's and mangrove Jacks cost approx EU€495 to build while the Mushulu 14's approx EU€650 and this includes all the requirements to forfill the standards. (Based on Australia's material costings)

in regards to storage within the seats, the actual storage compartment within each seat measures 24in by 18in (609mm x 457mm), not including the forward storage compartment. That's a lot of area or volume to store valuables or anything else for that matter.

Yes , we encapsulate all the plywood in epoxy. This ensure's that the boat has a long life as opposed to painting straight over bare ply. I've always felt that if your going to build a boat, spend the couple of extra dollars and do it properly. It also ensures that when it comes time to sell, you'll get a really good return of 2-3 times what it cost to build.

In regards to the standards that the boat is required to meet, this is included already in the plans price. Too Easy.!

Overall, thanks for your compliments Mike


I wonder if the contraction of air voids in foam in a cyclic way, will eventually de-grade the properties of the foam. Since the foam is rigid, and only so strong it must have some effect on the longetivity of the product. After all my empty gas tanks collapse into tiny round balls of plastic in the winter here (down to -40C) if I don't leave the vents open. G'day Clip,

The amount of air within the compartment isn't enough to create problems in extreme cold conditions. For example, take trawler freezers. They are made of foam glassed over and they go through enough cycles with freezing and defrosting.

Years ago we had a contract to maintain a fleet of 9 trawlers. During that 4 year period, the only time I had to work on a freezer was when the owner wanted to expand it size. Other than that, no problems. Also, if there was an issue, then foam core boats or freezers would not be built. I'm sure that if Sunseeker with their million dollar boats felt that there was a problem, they would not be touching the material.

Here in Oz on a hot day, you can see the plastic fuel tanks growing in size in the same way that I guess you see them contract in the cold. The foam filled bouyancy compartments didn't even move. I guess that say's something.

I hope this helps out.

regards
Mark

[Mike]

In regards to cost, its not at all expensive as one may think. The Mushulu 12's and mangrove Jacks cost approx EU€495 to build while the Mushulu 14's approx EU€650 and this includes all the requirements to forfill the standards. (Based on Australia's material costings)Mark

Methinks these costings you quote are either miscalculated or just plain wrong, irrespective of whether in Euros, GBP, or AUD. I would ask if your estimate includes the cost of BS1088 marine grade plywood, the epoxy and glass costs, fairing, painting and all other fixings and fittings to complete the boat without (that is, excluding) the 25HP outboard you use in your video to power your own build.

If you say it does include all these things then I think it's time for you to start exporting your materials, never mind your design plans! I would suggest then that you allow us to know what materials you say are required to complete the hull of any one of these three examples (Mangrove Jack, Mushulu 12 and Mushulu 14) so that we can make an accurate estimate of the cost to build here in the UK.

You may be somewhat taken aback once I have done such an exercise on your behalf for I can see no way a Brit backyardie could possibly build your boats for such low cost.

Sincerely

[bowdidgemarinedesigns]

Methinks these costings you quote are either miscalculated or just plain wrong, irrespective of whether in Euros, GBP, or AUD. I would ask if your estimate includes the cost of BS1088 marine grade plywood, the epoxy and glass costs, fairing, painting and all other fixings and fittings to complete the boat without (that is, excluding) the 25HP outboard you use in your video to power your own build.On our website, under each design, we provide a complete materials list so that people can cost the materials before purchasing the plans. Each client has provided us with their costings, based on their completed boats (using marine ply BS 1088), of which we compare with our own costings for each and every design. These costing can vary either up or down due to location or outlet, however are correct based on our clients costings and are not miscalculated or just plain wrong.

However, thanks for the compliment regarding "looking expensive", but I assure you, they are not expensive to build.

[Mike]

Well, well, well, what we have here is yet another example of an Australian designer who, when challenged upon some relatively important issue, runs away from sensible debate and just spits the dummy. Just as one of his predecessor Aussies did, Mark Bowdidge has petulantly run around abusing his privileges here and dumping his stuff into the ether.

Well, before I finish with commenting upon this characteristic, I would like to just quote from Mr Bowdidge's website as to material requirements to build just one of his designs, the Mangrove Jack. Here is what he says about the required materials.

MATERIALS LIST FOR THE MANGROVE JACK 3.65



The following list of materials is approximate and intended for calculation of approximate costs. We offer no guarantees of accuracy.
The list is for all timber in the construction of hull, deck and interior, including building stocks, temporary bracing etc. Allowance has been made in the quantities for about 20% wastage.
These figures allow for building with 1/4" (6mm) & 3/8" (9mm) Meranti, Hoop pine or Gaboon plywood for the hull and interior.
STRUCTURAL PLYWOOD OR PARTICLE BOARD
8ft by 4ft (2.44 x1.22m) 12mm (1/2") - 2 sheets
MARINE PLYWOOD
8'x4' (2.44x 1.22m - Pacific Maple or Gaboon)
6mm (1/4") - 7 sheets
9mm (3/8") - 1 sheet (Hoop Pine or similar)
SAWN PINE (for building stocks etc)
50X 75mm (2"x 3") (set up rails- use pine stud material) - 3.65m (12') x 2 plus 4 lengths of 553mm (1' 9") for the cradle crossbeams
Hoop Pine, Oregon or similar,
30x19mm (1-1/4"x3/4") (sheer clamps) -4 m (13') x 2
RESIN & GLASS (for coatings and reinforced areas)
Epoxy resin & Hardner -
West System, FGI R180/ H180 or Bote Cote - approx 15 litres
200g/sq.m cloth fabric - 13 sq.m (139 sq.ft)
Glue powder 5 kg
Fairing powder 2.5 kg (Q-cells, Microballoons or similar)
2 Litres of Part A High Density expandable foam
2 Litres of Part B High Density expandable foam
As anyone building boats here would know, the materials cost for just the marine grade ply and the epoxy resin required would far exceed Mr Bowdidge's estimate as to the total build cost. There is no need for me to go any further in proving that Mr Bowdidge's costs estimates made above in this thread are gross underestimates.

In fact, they are, in my view, very serious misrepresentations since they are made by one who claims to be an expert in the field and should know better.

For this reason alone, I have taken the necessary steps to halt Mark's vandalism on this website and to ensure that his statements in whatever is left of his posts remain in view for all to see. He is removed from this website permanently and his contributions are now in the trash can of 'dead' Aussie boat designers where he joins his fellow Aussie, Mik Storer, who was of similarly immature petulance.

Now, this thread has gone very far 'off topic' so my apologies to Paul who started it. I suggest we should ignore the input made by Mr Bowdidge and return to the subject of buoyancy. I would, however, ask members to carefully spell check their use of that word 'buoyancy'. Mr Bowdidge's various misspellings may have misled some of you to adopt his semi-illiteracy. It seems to me bizarre that a man who claims Associate membership of our RINA cannot spell the word 'buoyancy'. Hmm ...

Must say I am now disinclined to use that foam stuff on any boat I ever build. I will stick to using air for buoyancy, thank you very much. It is, of course, lighter than foam and has a superior buoyancy capability - and it costs nothing to use it.