I would appreciate opinions on the use of high density 2" single cell foam for bulkheads in a 16’ sea kayak. I know this is done by several high end kayak manufacturers. Pros and cons please. I am a long time professional boat builder and serious sea kayaker who will indulging a personal passion by building a limited number of high end kayaks each year.
100% bombproof sealing is hard to achieve with foam. In time they all come loose.
It is nice because it is soft and creates no stress risers.
Personally I like glassed in bulkheads.
Used it in my
Pungo 100, worked great. Cuts easy with a band saw and fine tuned it with sanding block.
on what the hull is made out of and the shape of the hull
Just add fore and aft…
…bulkheads on my Dagger Savannah. Got the 3" foam precut parts from Dagger. I used “Lexel” sealant to install. It is fairly easy to work with. Fingers dipped in soapy water allow nice smoothing of the Lexel bead. Working inside the boat is a little tight for some of the angles; but doable.
Does it work? I mean are the compartments dry? I don’t know yet. The Lexel needs to cure 2-4 weeks. So I won’t know for another 10 days. But it looks pretty good.
If your building…
Then you will more than likely be creating patterns, maintaining epoxy and dispensing pumps, pre-cutting panels, chines, decks or frames etc. Raw materials in some quantity at hand… 4 or 6 mm ply and 2 inch fiberglass tape would be light and leak proof. You can make patterns for fore and aft bulkheads, install them as a stage in the construction process. Foam works great for after-market and it can be installed leak proof but the labor would be same or greater than built-ins done during contruction.
What boats are you going to be building? Do you have a website up?
pros of foam bulkheads - they don’t create a stress point on the hull and they weigh less
cons of foam bulkheads - they leak and you can’t use them as a footbrace
What’s the difference in weight between a foam bulkhead and foot pegs and a fiberglass bulkhead that you brace off?
I’ll happily live with some spider cracking around the bulkheads and have dry compartments and a comfortable foot brace.
thanks for all the bulkhead comments
The boat will be a strong but light fiberglass composite hull and deck. The hull and deck themselves will NOT need or depend on structural strengthening from the bulkheads. I have been using marine sealant/adhesives long enough in my 30 year boat building career to know that I can surely get a good watertight seal. I will use Sikaflex 291, and the bond along the 2" outside edge of the foam and the hull and deck will be extremely strong and permanent. If the boat suffers impact damage on the bulkhead line then it should flex rather than stressing and cracking as it might do with a hard bulkhead.
The locatation of the fwd. bulkhead is far enough beyond the end of the foot braces that that even a 6’2" person can’t touch the bulkhead with his foot, so the problem of damage to the bulkhead from that shoudn’t arise.
I am NOT advocating foam bulkheads as the best solution by any means, just trying to weigh the merits of hard fiberglass bulkheads VS. high density foam rubber.
One of the issues is cost. From a manufacturers point of view, it will be much less expensive for me to install the rubber, and therefore less expensive in the long run to the customer.
More discussion and opinions are welcome. You can email me personally through my boat shop web page www.melonseed.com if you choose.
Thanks for the advice and comments.
my sense is that any issue of stress cracks at bulkheads is just as likely to manifest itself where there are NO bulkheads in the mid section of the hull where the greatest weight of the paddler can provide the greatest direct force against the largest area subject to flexing. If you’re building for light weight then it’s inevitable that there will be extra reinforcing around the seat area extending aft beyond the bulkhead. The loading that entry/exits/rescue impact the aft deck and aft edge of the coaming is sufficient that doubling the function of the aft bulkhead for structural reasons is common sense. If there was no aft bulkhead and you built the hull/deck to withstand those stresses where the hull is shallow/wide the glassing schedule would be much greater and beyond what would be necessary with a bulkhead that does double duty in reducing the compression of the hull at that area.
You build Melonseeds?
My Friend George has one. Fine boats. Nice work. I had the pleasure of meeting him and his wife out at a local lake for a day of sailing. It was mostly wooden wind for me but his melonseed took greater advantage of the light airs than my own home-built.
I can see how you would be able to ramp up for fiberglass boats… If they are anythig like the melon’s; They will be great boats. Looking forward to more info.
Hey, have you given any thought to a decked sailing canoe? If you could do that, say along the lines of Hugh horton’s and the Gougen Bro’s designs, you may find a niche. I would be a potential customer too.
I am not sure if I am anwering your question/concerns about structural strength, but for what it is worth there will be adequate strength in the deck and hull from a good laminate schedule using appropriate fabrics and viynlester resin. The hull will have carbon fiber reinforcements throughout, and the deck will be built incorporating foam sandwhich construction for light weight and superior strength. I am testing the strength of the hull and deck in prototypes now, and they will be built well enough to endure the challenges of re-entry etc, WITHOUT support from the bulkheads! In this case the bulkheads are primarily to provide the division of the boat into watertight sections. Based on that additional info does that make the high density rubber bulkheads more acceptable?
Yup, I build the Melonseed Skiff. So busy with them that I can’t imagine how I will even be able to make more than a handful of these kayaks a year, but they will be beauties!
The boat is somewhat like a ND Romany, but 7" longer and 1/2" wider (16’ 7" x 22") I expect it to be about 48 pounds. It’s a great looking boat with a sheer line to die for! She’s a looker! VERY seaworthy, easy to roll and extremely maneuverable while still a good tracker. Good initial and great secondary stability.
If you know how good the Melonseed is, well then that’s my benchmark for quality with this new kayak.
You are missing LeeG’s point entirely…
Are you seeking opinions or just looking to jumpstart your business? Awful lot of extra info spewed out at the first tap.
If you have been building boats for 30 years I figure you would already have this stuff figured out.....or at least experimented. Sounds more like you are building and then selling your experiments to the public.
Oh yea, Yes on foam.
one step forward, one step back
Here’s my $.01,it doesn’t matter, structurally speaking.
You appear to be asking the question steering back to one answer. You can make the deck and hull to have “adequate strength” (undefined) but there is a difference between point pressure on the aft deck caused by a 200lb person climbing on it, the hull withstanding a 200lb person getting in it on a flat surface, and the kayak getting dumped at the beach in dumping surf where the hull in it’s largest section takes the brunt of the load below the sheer where the hull turns in.
If you go and look at a bunch of old glass kayaks and where they have gel coat cracks/and glass failure you will probably find a lot of dings and damage unrelated to the bulkheads. Which tells me it’s a minor issue once you make the kayak of “adequate strength”.
I’ve got a friends carbon/kevlar racing kayak, no bulkheads but it has foam pillars for structural reasons and flotation. It’s dual purpose allowing for a 28lb kayak. Certainly it’s not meant for anything other than racing but it’s an indicator that dual use of a material doesn’t reflect a failing or lack of strength.
"but for what it is worth there will be adequate strength in the deck and hull from a good laminate schedule using appropriate fabrics and viynlester resin. The hull will have carbon fiber reinforcements throughout, and the deck will be built incorporating foam sandwhich construction for light weight and superior strength. I am testing the strength of the hull and deck in prototypes now, and they will be built well enough to endure the challenges of re-entry etc, WITHOUT support from the bulkheads!
He is simply asking questions
"Acknowledge your fellow human beings out there with a smile and consideration"
I’m no expert
this is just an observation as someone who’s worked at a couple paddle shops and made a few s&g kayaks. Flexible polyethelene hulls have a hard time keeping bulkheads waterproof over time.
Hulls rigid enough for “average use” appear to have enough strength at any particular point below the waterline that it’s pretty much a random walk whether the theoretical impact at the point where a stress riser can occur will actually result in a more catastrophic failure than the same spot with a softer bulkhead.
Imagine someone dragging a kayak off of a rack or over a log,at some point all the weight of the kayak is resting on a cross piece. The hull is naturally stiffer up by the forward bulkhead, the hull bottom is most likely to flex right in the middle. If there’s enough weight in the kayak the significance of hull rigidity will mostl likely be experienced in the middle of the hull. If the stress is great enough that there would be cracking/damage it will most likely occure before or after the hard/soft bulkhead anyway, if there’s enough PSI loading in a small area it’ll be the strenght of the composite WHEREVER the impact is, not just those two strips where the bulkheads are.
Think of a skin boat and all those stress risers, they’re everywhere! So if you make the minicell bulkhead sufficiently thick to resist displacement by an occasional drybag or the hydraulics in a wet exit in the surf it’s probably contributing some resistance to compression whether you want it or not.
My take on it is that flexible bulkheads make sense for flexible hulls, if the hull isn’t very flexible and you’re using high tensile materials then any failure will be catastrophic anyway so a rigid bulkhead wouldn’t matter and would allow for more storage space. If you’re using high tensile materials that are thin and flexing then minicell makes sense but I bet that if you used rigid bulkheads you’d find cracking in the hull from regular use/transport that have little to do with bulkheads.
This is a round about way of saying check out some of the stiffer minicell from JR Sweet for the aft bulkhead.
No jumpstarts here!
Easy man. Been building sailboats for 30 years, but lightweight strength to weight technology and engineering in kayaks is a whole new game for me. I am only trying to seek input from, and exchanging ideas with those MORE informed than I in this area. Nothing commercial here, just honest curiosity and enthusiasm for the project. Besides, only being able to find time to build a few of these a year is hardly likely to be a profitable enterprise, just fun.
this forum is for info
very cool that you are seeking input from the knowledge base. my opinion is to glass ply bulkheads in place, more elegant
for one off construction a 48lb kayak could be nearly bombproof. How about carbon/s-glass cloth in the hull/deck where it’s fattest from a bit behind the aft bulkhead to the front bulkhead. The carbon is oriented widthways with the s-glass lengthways. Maybe another layer of carbon/kevlar on the inside and a layer of s-glass on the outside with doubled layers of heavier s-glass on the bottom of the hull. And that coremat where ever but looking at the use of unidirectional materials of the proper weight before looking at coremat like materials.
I’m making this up,Onno should weigh in here.