Foam Core D15? Or some thing else?

Power Boats only. Please include the boat type in your question.
badknotguy
New Poster
New Poster
Posts: 5
Joined: Thu Dec 05, 2019 8:45 am
Location: FL

Foam Core D15? Or some thing else?

Post by badknotguy »

Hey everyone, thanks for posting all this great information on these forums. It has been very helpful in planning out my next build. I am still very much in the planning phase but am ready to begin construction on something soon.... what it is however remains to be seen. For a little back ground before I get to the key question below I do have experience with wooden boat building.... I have built a CLC kayak from a kit and a boat builder central GF16 from scratch. I have also done a major renovation on a Gheenoe and a flat skiff 12 bottom replacement so I do know my way around the skills and techniques for building with wood reasonably well. Always trying to learn more though.

The scenario for the next build is something that I can work on over the next 16 months while I am taking grad school classes. It will be an intermittent build between classes and work so it needs to be simple design from the construction and rigging perspective (it will be tiller). The boat will be fished in the 10K islands of SWFL in largely protected water. Occasionally ducking out to 10K beaches to fish in the summertime. Mostly sticking to the mid and back bays though.

I currently have a 15hp Mercury EFI hanging on a Towee scout in the garage. When this build is done the Towee will get sold and I will either keep the motor or sell it with the Towee and pour the money into powering up whatever I have built. I do like the Merc and would prefer to keep it. It matches well with the type of fishing I do (back country). It is light, reliable so far, and easy to use.

So with all that being said one of the options I am looking hard at is a D15 build in foam core. I like the idea of foam because I have never built with it before and would like to try it out. I understand it is more expensive and will take far more epoxy and glass to get the equivalent strength of a wood core boat. I do like the Chris Morejohn builds but they aren't simple enough for the time I will be able to devote and I don't want to end up with an orphaned project.

Here is the base recipe I am considering for the foam core build.....

3/4 Divinycell H80 for hull bottom and sides
Hybrid Coosa/Aquaplas/H80 Transom - some variation of sandwich with glass skins and maybe interior laminations.
For the skin - I am considering going with the 3 layers of 10oz. E-glass like the Morejohn builds call for - Just because I could be certain it would be stout. Probably overkill. Definitely a pain in the rear to glass. At least 10oz. goes down so nicely.
The interior layout would be a rear bench/deck
Low front deck
H80 breasthook and knees
Highly likely to lay a second layer of scored 3/4" H80 down on the floor span between the rear and front decks for stiffness and floatation.
I would probably do a 2" H80 strip for rub rails and maybe even another for an inwale to stiffen it up.

So my question is - is this a dumb idea? What would you change on the build schedule above? Should I just get an FS18 kit? I am attracted to the D15 because the higher freeboard and sweet dory lines. Plus my garage is shallow - a 16 ft. hull can go straight back with a swing tongue trailer but and 18 footer would need to go at a hard angle. At least my wife gave up on parking in the garage long ago.

The boat would spend ample time being poled so maybe an FS18 makes more sense. If I go that route I would just buy the wood kit. Or probably even better an LM18 kit and a new motor (ouch). Budget for the hull build would hopefully be kept under 3K. An LM18 would break that although I think if I go the D15 or FS18 route I should be able to do it. The FS and LM 18 builds are more complex and thus I would want to do it kit - and that adds expense.

Looking for a sanity check/second opinions. Thank you all for your time!

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10199
Joined: Tue Jan 12, 2010 12:25 am

Re: Foam Core D15? Or some thing else?

Post by fallguy1000 »

The main thing to reconcile is how will the foam be supported throighout the build and how can you flip wothout shape loss.

How do you plan to build and flip and what will hold the hull shape diring the flip. Eye trouble at noght for me so I do my best.
My boat build is here -------->

viewtopic.php?f=12&t=62495

badknotguy
New Poster
New Poster
Posts: 5
Joined: Thu Dec 05, 2019 8:45 am
Location: FL

Re: Foam Core D15? Or some thing else?

Post by badknotguy »

Good question. I would build MDF molds using the frame templates included in the plans and probably do a couple of "free style" supports to for the flip too. I would build it upside down to start and take it all the way to the primer stage before I flipped. At that point and given the relative simplicity of the build (and light weight) I would hope I could figure something out once flipped.

Fuzz
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 8921
Joined: Tue Aug 02, 2011 4:23 am
Location: Kasilof, Alaska

Re: Foam Core D15? Or some thing else?

Post by Fuzz »

For either of those boats 3/4 H80 is way over kill for the sides. The bottom takes the stress and the sides keep the water out. well they do more than that but you get the point. I would probably use something like 3/8 H60 for the sides. If you go foam I think JM would give you a lamination schedule.

Jeff
Site Admin
Site Admin
Posts: 8436
Joined: Fri Apr 29, 2016 12:17 pm
Location: Vero Beach

Re: Foam Core D15? Or some thing else?

Post by Jeff »

badknotguy, welcome!! Tough decision to make!! Both the FS18 and LM18 are great boats and the CNC Kits gives you a real good head start on the build!! Jeff

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10199
Joined: Tue Jan 12, 2010 12:25 am

Re: Foam Core D15? Or some thing else?

Post by fallguy1000 »

Fuzz wrote: Tue Jan 26, 2021 3:18 am For either of those boats 3/4 H80 is way over kill for the sides. The bottom takes the stress and the sides keep the water out. well they do more than that but you get the point. I would probably use something like 3/8 H60 for the sides. If you go foam I think JM would give you a lamination schedule.
Yes. David is correct. I could barely see this last night. I am getting some late night eye fatigue? Bitch gettin old. 3/4" is major overkill unless the lighter glass can achieve something going heavier. Shear becomes an issue in glass specs and is above my pay grade. But light glass may present some issues when not combined with others. Also, keep in mind a 5 oz glass strand oriented only 0/90 is not as good as say two 6 oz 45/45 and two 5 oz 0/90, so some glass combination is probably required. Unis are even better, but they have the issue of not finishing as nice. Glass selection is complicated business. I only know one guy in the Philippines that is really good at it and even he tends to overbuild.

The foam will be provided by designer.

The inside of the foam will require lamination prior to laying on the mould. Foam has zero support across a foot. Not sure about the 10 oz woven. While it finishes nice; it isn't too stiff and the panels may not lay flat and sag between the moulds; if say the moulds are 18" apart.
My boat build is here -------->

viewtopic.php?f=12&t=62495

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10199
Joined: Tue Jan 12, 2010 12:25 am

Re: Foam Core D15? Or some thing else?

Post by fallguy1000 »

You may need to install rubrails or beef up the top edge of the gunwhale. I do not know how Jacques is dealing with the flip question in his foam book, but a foam boat is very floppy and can lose shape easily when removed from the jig.

It may require a temporary bottom jig even to avoid getting the dreaded hook. I just see a potential for troubles.

The absolute best way would be to light glass the exterior and build the foam boat in a female jig. That way the bulkheads and stringers and floors go in; then the boat is flipped for final glass, fairing, paint, then reflipped for sole and finishing the inside.

This might upset a few applecarts, but I have gone through all of this many weeks in my brain and in consult with other builders. I am not saying foam boats cannot be built on male moulds; I am saying what is best is all.
My boat build is here -------->

viewtopic.php?f=12&t=62495

badknotguy
New Poster
New Poster
Posts: 5
Joined: Thu Dec 05, 2019 8:45 am
Location: FL

Re: Foam Core D15? Or some thing else?

Post by badknotguy »

Thanks guys, I appreciate all of this. The reason for theoretically using all 3/4” foam is very simple....volume discounts from my local supplier. My cost on 7 sheets of 3/4 would be less than a combo of various sizes (the price break is at 5 uniform sheets). In theory the thicker foam would also help with some of these jig issues. Running a jig support from bow to stern would not be out of the question on a male jig, especially given the relative ease in adding it. Foam sounds like it has been hard to come by lately too so that could torpedo this idea. If I can’t get it I can’t build it! Lots to think about, thanks again.

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10199
Joined: Tue Jan 12, 2010 12:25 am

Re: Foam Core D15? Or some thing else?

Post by fallguy1000 »

badknotguy wrote: Tue Jan 26, 2021 9:45 am Thanks guys, I appreciate all of this. The reason for theoretically using all 3/4” foam is very simple....volume discounts from my local supplier. My cost on 7 sheets of 3/4 would be less than a combo of various sizes (the price break is at 5 uniform sheets). In theory the thicker foam would also help with some of these jig issues. Running a jig support from bow to stern would not be out of the question on a male jig, especially given the relative ease in adding it. Foam sounds like it has been hard to come by lately too so that could torpedo this idea. If I can’t get it I can’t build it! Lots to think about, thanks again.
Well, the bow to stern jig is for the female side; not the male, so once flipped; the boat may be best served by holding the correct bottom shape.

Foam of 3/4" sounds rather thick. I am surprised 3/4 is the spec and wouldn't the price break apply to 5x1/2" or have I missed a bottom spec of 3/4".
My boat build is here -------->

viewtopic.php?f=12&t=62495

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10199
Joined: Tue Jan 12, 2010 12:25 am

Re: Foam Core D15? Or some thing else?

Post by fallguy1000 »

Most of the time a person is going to need to walk into the boat for stringer work and such. That load could result in changing the shape unless the bottom keel tapes are enough. All I am saying is there is a risk with light glass.
My boat build is here -------->

viewtopic.php?f=12&t=62495

Post Reply

Who is online

Users browsing this forum: Google [Bot] and 16 guests