Reinforcing a mono under the bow suggestions

[Kaotic]

I'm building a 35" mono and usually I just use CF for added strength. But this time I want there to be some more strength but with little added weight up under the bow area.

My original plan was to use pink foam board and make a 2"-3" wide beam that ran the length of the bow from bottom to top, but I'm having a hard time shaping it to have a nice snug fit. I was also thinking of making a CF bulkhead, but that would only strengthen a small area. I also don't want to mess with the 2 part expanding foam, because I've read mixed reviews...

So my question is, does anyone have any other suggestions??

Thanks!

[Kaotic]

I was trying to think of a way I could make some kind of cast on the inside but only a 2"-3" wide section then pull it out and trace it on to a piece of pink foam board then it would be to the exact shape. Then glue it in. I was thinking of trying some sort of clay, anyone know of some kind of material that could be used that can be moulded by hands but doesn't cure/dry???

[RaceMechaniX]

I have used 2 part expanding foam with good success in mono's. Yes it is a little messy, but it stiffens the entire bow and provides you with the necessary flotation. The trick I use is to mix small batches of foam in 4OZ cups. Pour the foam in the nose and then rotate and tip the hull so the foam spreads as much as possible. This controls the build up to a certain extent and prevents the common bulging due to pressure. Repeat in till you have enough foam in the nose. Leave 1-2 hours between pours to ensure the foam has cured enough. I use 3lb foam from US composites. http://www.uscomposites.com/foam.html It is light enough to not add significant weight, but dense enough not to crush.

Again small batches and allow the foam to spread by rolling and tipping after you have poured it in.

TG

[Rocstar]

I have used 2 part expanding foam with good success in mono's. Yes it is a little messy, but it stiffens the entire bow and provides you with the necessary flotation. The trick I use is to mix small batches of foam in 4OZ cups. Pour the foam in the nose and then rotate and tip the hull so the foam spreads as much as possible. This controls the build up to a certain extent and prevents the common bulging due to pressure. Repeat in till you have enough foam in the nose. Leave 1-2 hours between pours to ensure the foam has cured enough. I use 3lb foam from US composites. http://www.uscomposites.com/foam.html It is light enough to not add significant weight, but dense enough not to crush.

Again small batches and allow the foam to spread by rolling and tipping after you have poured it in.

TG

+1

Jeff, I've done bulkheads and other methods in a few builds, the 2 part foam is by far the easiest route and supports the deck the most. Going slow like Tyler mentioned is the only way it works. The only down side is performing any repairs if the hull gets damaged is difficult. But at the speeds we run at a hard crash usually destroys the hull anyway....

[Kaotic]

Thanks Tyler! One of my biggest concerns is the added weight, I was looking at the 2lb one and it says it adds 2lbs of weight per cubic foot. So I'm guessing I would probably use roughly .75 cubic feet so close to 1.5lbs extra sitting up front. Did you find it to add a lot of weight?

I was thinking of wedging in that pink foam board in as much of the bow as I could then leave a 1" gap between the pink board and the top then pour in the 2 part foam to fill up the gap(s). My thought is it would still be strong but save a lot of weight. Any thoughts on that method??

[Kaotic]

+1

Jeff, I've done bulkheads and other methods in a few builds, the 2 part foam is by far the easiest route and supports the deck the most. Going slow like Tyler mentioned is the only way it works. The only down side is performing any repairs if the hull gets damaged is difficult. But at the speeds we run at a hard crash usually destroys the hull anyway....

Thanks Joel! I want to do the 2 part foam so bad just because It seems easy and of course would add the most amount of strength. I just can't get past adding 2 more pounds of weight, this 35" boat it already coming in at over 11lbs.

Joel what do you think about my idea of doing as much pink board as I can wedge/glue in there then pour the 2part stuff in between the top and the pink board an inch below??

[Rocstar]

Thanks Joel! I want to do the 2 part foam so bad just because It seems easy and of course would add the most amount of strength. I just can't get past adding 2 more pounds of weight, this 35" boat it already coming in at over 11lbs.

Joel what do you think about my idea of doing as much pink board as I can wedge/glue in there then pour the 2part stuff in between the top and the pink board an inch below??

Don't see why it wouldn't work.

[Kaotic]

Update:

I ended up just doing the 2 part foam with no pink foam and it worked out nicely. I didn't fill it all the way to where the hatch opening is, I stopped about 4” shy. It added 5.9oz of weight to the hull. I took your advice Tyler, and did 5 or 6, 1.5-2oz pours every 1.5 hours and moved the hull around to get it to cover more area when I first poured it in that really helped I think too. I did this in a bathroom where I stuck a big space in a few hours before and got the temperature up to 88-90 degrees, which I guess lets it expand more and cures faster.
Its been maybe a week since I did it, and the bow is solid with now distortion and no shrinkage that I can see.

[RaceMechaniX]

Good to hear Kaotic,

You might consider adding more foam once everything else is installed along the seams on either side from the transom forward. This will help stiffen the sides considerably.

See pics for reference.

TG

DSC_4295.jpgDSCN9730.jpg

[Kaotic]

Good to hear Kaotic,

You might consider adding more foam once everything else is installed along the seams on either side from the transom forward. This will help stiffen the sides considerably.

See pics for reference.

TG

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Thanks Tyler, I believe I saw you did it in your DF Sniper as well. I was thinking about it, but I'm so over concerned with the total weight of this hull that I want to wait until I run it a few times once its finished (which should be in roughly 2 weeks). Then if I'm in the ball park of what kind of speeds I want out of it, then I'll add some foam for added stiffness along with beefing up my stringers.

I wish I could just forget about what this build weighs, but my other hobby is building competition mountain bikes and in that hobby we measure weight in grams lol

[RaceMechaniX]

Weight typically does not hurt the DF hulls as much as you think. They tend to lift just fine particularly at high speed. My N2/P SAW mono was pretty heavy and still managed 76 and 80mph respectively.

TG