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Corecell foam double ender Briggs

Posted by MJones 
Corecell foam double ender Briggs
July 19, 2011 08:48PM
Currently building a double ender Briggs (17'10" oal, 55" bottom). Dimensions evolved from Andy's patterns. All panels are 3/8" Corecell foam. Put a false floor in the bow passenger footwell to make it more friendly for fishing. Borrowed Brad's self-bailing idea for passenger seats and rower footwell. Wanted to get the water to drain faster than the traditional hose and thru-hull. Would still like to be able to bail rear passenger footwell for when there is no passenger, but have not come up with a bilge pump system that looks clean.

Went with the wide bottom and foam in order to get the draft down.

Will try to post more pics as it progresses.

Re: Corecell foam double ender Briggs
July 19, 2011 09:29PM
Please do keep us posted. I love steps-along-the-way boat building photos.
I need to find better forum software, that lets members keep a separate blog if they want.

I wish there was some way to compare Corecell foam to Plascore. I suppose there is.
I'll just have to buy some and glass up some test panels. Where or who do you buy the Corecell from?

Re: Corecell foam double ender Briggs
July 19, 2011 10:26PM

Haven't heard much from you in a while.

Looks like a great project and major progress so far. After just completing 2 composite boats I would like to keep learning. There are fabrication issues with honeycomb core. While it's light, weight isn't everything. I have started looking into foam also. I have a feeling that a mix of materials may yield good results.

Where can I find specs for corecell, density etc.? What thickness are you using? Please keep us posted as I am sure we all have a good chance to benefit from what you learn along the way.

It looks great so far.

Re: Corecell foam double ender Briggs
July 20, 2011 01:01AM
Following are the sites for source and specifications. The 3/8" foam is easy to work with, cuts with razor knife. Just guessing Larry, but I would think it uses less epoxy than plascore on account of the surface smoothness and edge filling (does plascore have a slight dimple surface?). Precoated with epoxy/cabosil mix and let tack up, then started glass lamination (same as plywood). Do keep corecell flat when storing. Will stay in touch and lets get on the river.


Re: Corecell foam double ender Briggs
July 20, 2011 04:22AM
Yes, please do keep us posted through the build.
I am working out details of a bigger white water dory built from alternative products myself, although I will still have some wood because I feel safer with wood more so than other products. The idea is light weight with a wood look.
I am definately interested in how the corecell foam works out and any "humps" you may encounter building with it.

Re: Corecell foam double ender Briggs
July 26, 2011 01:47AM
Couple more pics of progress, think I see an end in sight. Must take a break the next few days, headed for the river.

Re: Corecell foam double ender Briggs
July 26, 2011 02:58AM

It looks very clean. What is the white around the joints? Are you using some kind of white filler or glass bubbles? I like the drain tunnel for the foot well. Much simpler then the hoses and fitting I have been using and the flow will be much better. I am going to do it on my next boat. I'll pay you a small royalty.

What do you plan for your gunwale design? With plascore I kept the inside and outside gunwales 1/2 inch above the plascore edge. I then filled the gap with 1/2X1/2 strips. Not the best idea. As the wood moves with weather exposure it brakes the epoxy joints. Once cracks start they grow quickly. Need to fine a better solution.

I am looking for some scrap Trex decking to scarf and epoxy up. Wonder if it might be an option for gunwales instead of oak or ash. It does great in sun and rain with no need for finish.

Re: Corecell foam double ender Briggs
July 26, 2011 04:27AM
Just used cabosil mixture for fillets, and cabosil/qcell (glass bubbles) for fairing. No royalty needed for me, just send to Brad Dimmock, borrowed drain idea from him. Gunwales are going to be oiled teak, refuse to put anymore varnish on a river boat. Edge of foam will be routed out between glass and filled with epoxy and then that thin strip will be painted teak brown.

Laminated up foam to make gutters for hatches and then routered out. Trying to eliminate all wood with the exception of the stem posts and teak trim.

Trex seems pretty heavy, why not use 3/4 x 2 corecell sheathed? Paint it a teak brown and have no maintenance. Some of the large sportfish boats have been doing there toerails out of foam and then painting to look like teak from a distance (doesn't look bad).
Re: Corecell foam double ender Briggs
July 26, 2011 09:00AM
I plan to make a Plascore "ledge top" gunwale, where a continuous 4" horizontal arc of Plascore--from front to rear on both sides--joins the top edge of the side panel with biscuits and goo. I'll round the two exposed edges on the horizontal gunwale-arc, putty them and wrap the whole thing with glass tape. The horizontal arc makes it stiff. And it will be quite light compared to hardwood. Four 3/4" by 2" ash strips are heavy just to pick up. Add spacer blocks, bolts nuts and washers and put all of that on a light hull and it suddenly isn't so light any more.

I have made these ledge top gunwales several times using end grain balsa blocks. More recently I made a 3/8" thick by 4" wide plywood ledge-top gunwale. They do work just fine and they are a lot lighter than the 11 board feet (or so) of hardwood it takes to make wood gunwales with 3/4" x 2" x 16' stock, especially so when white oak or ash is used instead of fir.

Plywood ledge tops are a bit easier to work with than plascore. But I'm done with plywood now. I'd like to experiment some with Corecell foam--perhaps for seats and locker parts as a starting point. I do think Plascore is the way to go for stiff but light weight gunwales.

Re: Corecell foam double ender Briggs
July 26, 2011 02:01PM
Have you glued Teak before?

I used it once and many said it does not glue well. I cut the piece and cleaned it with acetone just before the epoxy went on. I had no trouble with the joint but is was also not under load like a scarf on a gunwale.

That was a few years ago and it was expensive then. A wood worked I know got a piece about 2 years ago for a kitchen job and the price was ridiculous by then.

While I really like the look of the clear finished boats, they just don't hold up. Having inside storage will extend the finish for many years but it there is no garage or boat cover then it is pointless.

One of the people I share shop space with said he learned from a veneer worker that 1/8 inch stock was the point where glue bonds cause trouble. Glue bonds are stronger then wood grain and with thin stock the wood will stretch but, glue 2 peices of wood together which are 1/2 inch thick and the expansion of the wood will work against the glue bonds which will not fail. Over time the constant movement causes cracks to develop.

While a classic all mahogany power boat for cruising might be worth the endless time it takes to keep it looking like a gem, trying to do it on a working river boat just doesn't work out.

You are correct about trex, it is very heavy. I will need keep looking. There are a lot of problems we seem to solve but with a large price in time which, often keeps us off the river and in the shop
Re: Corecell foam double ender Briggs
July 26, 2011 04:13PM
Ash weighs 3.5 pounds per board foot. 11 board feet (I think I got that right) would be almost 35 pounds, just for the gunwales on the 16' side panel of a 15' boat. More for a 17 footer.

Here's a 3/8" plywood ledge top. I think I'm going to like 3/4" Plascore better.

Just thinking out loud here......Larry. If you have a fixed-in-place side-to-side deck (like your new white water boat) what do you need a gunwale for?

Re: Corecell foam double ender Briggs
July 26, 2011 06:00PM
That's a good looking boat sandy , the ledge really is A good finishing touch , and I bet the hole boat is stiffer and stronger.
Re: Corecell foam double ender Briggs
July 27, 2011 02:46PM
How about PVC or irrigation pipe or some plastic hose, if you want a 'quick and dirty' easy to make and maintenance free gunwale? Anything with a round cross-section that will conform to the shape of the hull without 'waves' or kinks. Slit it or cut a slot and push it down on the top of your hull layup, then glass over the shape for the strength. If you wanted extra strength you could use carbon fiber tows before you glass over it. Something like that would make it easy to dump the water from the boat and provide good hand holds...super light, too and cheap.

Me, I would use raw teak. It has the best 'grip' and if you let it weather naturally, it turns an attractive silver..Cheaper than Trex, too.
Also, FYI..you can put a durable bright finish on teak. What you do is after sanding, you wipe it with acetone and roll/brush on some WEST epoxy. Sand again and another WEST coat, then varnish as you choose...with a UV resistant varnish. The WEST undercoat will make the finish last at least a full season and a quick rub with some Scotchbright or some 120-150 sandpaper will have it ready for a new coat of varnish without having to take it back to bare wood.
Re: Corecell foam double ender Briggs
July 27, 2011 02:58PM
This is a fun and interesting thread. It took me a while to get the following question to bubble up to the top of my conciousness:

You are making a decked boat. So what do you need a gunwale for anyway?
I'll re-phrase that more emphatically:

Eliminate the gunwale. The purpose of the gunwale is to make the top edge of the boat stiff.
But the deck and the various compartment partitions on a decked white water do that already. Zap the gunwale. You might have to stiffen things up a bit where the oarlocks go. But in the general case, you do not need a gunwale anyway.

I have never built a decked boat. So in that sense I don't know what I'm talking about. But my cocky arrogant and overly-self-important experience tells me what I said above is correct. A decked boat does not need a gunwale.

Re: Corecell foam double ender Briggs
July 27, 2011 06:01PM
I saw your question and started to think about it and then forgot to respond.

The gunwale add a lot of stiffness at the oar location. In the case of my plascore sides, if it was not there what would stop the side from folding over if it hit a wall? I we crab an oar will the side material be strong enough? If one of those super heavy ash oars can have the shaft snap what would happen if strong gunwales were not there? I have seen 5/8 bronze oar locks shafts bend. I have seen steel frames from rafts bent after flips.

Then there is the issue of attachment points for static line or webbing if the sucker gets pinned. There might be options to replace the gunwales but I have not thought about them much.

A lot of us are working on some different ideas. I have spent a lot of time working on the idea of floor flex and have still not solved some of the problems. It might be faster and more practical to deal with floor impact damage by going up to 4/4 or even 6 quarter plascore bottoms. Jeremy has installed a 1 inch plascore bottom on his current project.

Sadly not many people are willing to dig in. Most just want to keep building what has been designed by someone else.

Re: Corecell foam double ender Briggs
July 27, 2011 06:49PM
I understand your question: "The gunwale adds a lot of stiffness at the oar location. In the case of my plascore sides, if it was not there what would stop the side from folding over if it hit a wall?"

I have built glass and balsa-core gunwales that were lighter overall than four long wooden strips.
I added a LOT of glass in the oarlock area. But still saved weight overall. So now I'm thinking a decked boat could eliminate the gunwale altogether, if you sufficiently stiffened the oarlock area. Somehow. Someway. And in a way that does save weight overall.

Aluminum tower oarlock pins (like Jeremy once used in his Desolation HD) could be used too. You'd have to go to some length to strengthen and stiffen the spot where those attach, if you did it that way.

I'm just thinking you could save some weight overall. Yes it's true. Most first or second time boat builders want to do what's known work--without having to experiment with anything. But after boat number 3 or 4 the interesting part is fiddling with the details....trying new ideas is what keeps me thinking about it. The lightest possible boat still stiff enough and strong enough to make a good boat is what I'm interested in most.

It does seem to me that 25 - 35 pounds of gunwales (depending on wood choice, whose only purpose is to make the oarlock area stout enough) is overkill....at least for a decked boat. For an open boat there may be no alternative to a gunwale of some sort. But even in the open boat case there are ways to save weight (like a 3/4" or 1" Plascore ledge top instead of wood strip gunwales).

Re: Corecell foam double ender Briggs
July 27, 2011 07:00PM
Last week I got my shipment of 12 gallons of epoxy from Raka. So I am ready to embark on my all plascore honky dory build. I will keep you all posted on how it goes. I am going to do a 4/4 plascore floor, but it will be with 2 layers 1/2 layers of plascore with kevlar between and fiberglass on the outside. maybe it will be so stiff that I can get away with not floating the floors like Larry has done. It would make construction easier. I will have to do some stiffness testing.

I also want to test if I can put t-nuts between the sheets to create threaded anchor locations. That might give some flexibility for modular designs. Got to test how strong those would be too.

Re: Corecell foam double ender Briggs
July 27, 2011 08:15PM
Here's my take on the no-gunwales decked boat (after thinking about it a bit more).

Make the deck dead level with the top edge of the side panel. Then there is nothing to "fold over"
if you jamb an oar against a canyon wall. Make an oarlock holder something like this:

In the photo above, imagine the flat plywood ledge-top gunwale as the deck. Instead of extending 4" inward, imagine it extending all the way across the top of the boat, continuously, from side to side. Now the top edge of the side panel is as stiff as it gets. You had to build the deck anyway. And now you have no gunwale at all.

And now you can now add a semi-decorative Plascore lip up a an inch or two from that stout top-side edge, just to keep stuff
from rolling off the deck.

Re: Corecell foam double ender Briggs
July 27, 2011 11:14PM
After my last post I took the trailer down to the shop in Salt Lake for Jeremy to pickup.

On the way I started thinking about your no gunwale idea. While it seemed strange at first the more I think about it the more I see it as workable. The only issue is the oarlock socket. Your photo is one approach to start thinking about.

Like you suggest we can have the deck at the top level and glass over the edge just like we do on the chine.

The only problem I see is that it might make the boat too ugly to look at.

I just moved out of my shop. What am I to do now? All these great ideas are coming along and I need to start another boat.

Re: Corecell foam double ender Briggs
July 28, 2011 03:12AM
....jack your house up 8' on stilts....and then build walls around the stilts, and call it a house on a shop?

Re: Corecell foam double ender Briggs
July 28, 2011 02:22PM
If you built a boat with a ledge-top gunwale, then you could make the deck removable. The deck would contain integral, built-in storage compartments whose compartment bottom extend down to about an inch off the floor of the boat. Those compartment bottoms could have soft rubber gaskets glued to the bottom, so they snug up against the bottom of the boat. Then you'd have some flex in the bottom.

You'd want to fine-tune the bottom flex so it was essentially stiff and immovable under normal rowing conditions, but so it had enough flex to give (rather than fracturing) when you smash one of those nasty mid-river boulders--lying hidden two inches below the muddy desert white water surface.

The removable deck would bolt down onto a rubber gasket between deck and ledge top. Even if you end up fishing with the deck still in place most of the time, a removable deck (with integral, built-in compartments) would make hull maintenance a lot easier.

Re: Corecell foam double ender Briggs
November 24, 2011 04:35AM
Corecell M80 9.5mm

Attached is latest picture, getting ready to paint. Almost entirely foam except for teak gunnels and bow and stern posts. Even gutters for hatches are foam, not sure I would do again as it involved a lot of additional labor hours.

Happy holidays!

Re: Corecell foam double ender Briggs
November 24, 2011 08:25PM
That looks great, did you get that foam in 4x8 sheets and scarf them ? The other question I had was what thickness you used and how much it cost per sheet. That stuff looks like a great material , I just have not heard much about it.
Re: Corecell foam double ender Briggs
November 28, 2011 03:51AM
Panel thickness is @3/8 and comes in 4x8 sheets. If I remember correct, sheets were around $120. No scarfing necessary, just butt joint, strength is in the sheathing. Panels plenty rigid once glassed. Hatches have a second layer of foam sheathed on under side, most of the guys use plywood here, but my goal was to use little or no wood. Larry, for the gunnels I routered out the foam edge and filled with epoxy. Will paint this strip teak brown to try and match the teak. By the way, the teak steam bent and epoxied on with no problems. Did have to steam it though as it felt like it might snap when dry fitting.

Many thanks to Andy H. and others for all there input during the build.

Re: Corecell foam double ender Briggs
November 30, 2011 07:06AM
Did you use 3/8 for the bottom?
Re: Corecell foam double ender Briggs
November 30, 2011 08:14PM
Used 3/8 for everything. Should weigh in around 320#, will let you know once complete. Think 1/2 would work just find also, whatever you find a deal on.
Re: Corecell foam double ender Briggs
December 06, 2011 03:27AM
Just another pic of hull flipped. Still need to make handrails from leftover teak and source nylon insert for aluminum oarlocks. Slowly coming to an end, looking forward to a shake down float on the Bighorn next month.

Re: Corecell foam double ender Briggs
December 06, 2011 05:45PM
That's a damn fine looking boat.
Do you know what it weighs yet?

I have a 500lb scale I can hang boats from.
Another way (if you want to know) is to go to an grain terminal (where you can by cattle feed).
Weigh the boat and the trailer.
Then weigh the trailer only and subtract.

A traditionally-framed Briggs, with all those compartments, would be heavy.
It would be interesting to know the weight of yours.

Re: Corecell foam double ender Briggs
December 06, 2011 07:21PM
Tungsten: I steam bent gunnel and epoxied on, will be adding silicon bronze machine screws with grommet nuts (sex nut).

Sandy: thanks for the feed store scale idea, I will do that and let you know. Andy's which is very similar came in around 320#.
Re: Corecell foam double ender Briggs
December 18, 2011 10:23PM
Just a couple more pics, still doing the finnish work.

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