1981 Dolphin 20' Commercial

Questions about boat repairs with our resins and fiberglass: hull patches, transoms and stringers, foam, rot etc.
MSRiver
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Re: 1981 Dolphin 20' Commercial

Post by MSRiver »

Would this not be the perfect example and area to use of the composite parts? Looking at composite part 2208 particularly, should fit just right and a quick solution?!

Fuzz
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Re: 1981 Dolphin 20' Commercial

Post by Fuzz »

I am not sure what 2208 is but anything to help stiffen that area and spread the weight would help. If you can feel it flexing from just walking it needs some help. Stringers or bulkheads something to make the unsupported areas smaller.

MSRiver
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Re: 1981 Dolphin 20' Commercial

Post by MSRiver »

the composite beams they sell here.

https://www.boatbuildercentral.com/prod ... form_Beams

fallguy1000
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Re: 1981 Dolphin 20' Commercial

Post by fallguy1000 »

I can't quite follow the question.

If you are trying to make spans less; then those beams look good, but they need to be taped underneath or span across a BH or floor.

Also, you can just sister onto the floors and bulkheads existing with 3/4" lumber for more edge for glue surface

I find that any span over about 18" gets squirrely with 1/2" plywood glassed lightly.

But you really need to determine the span you are willing to deal with...testing is how...
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Fuzz
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Re: 1981 Dolphin 20' Commercial

Post by Fuzz »

Those beams would work just fine for this.

MSRiver
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Re: 1981 Dolphin 20' Commercial

Post by MSRiver »

Got those beams put in yesterday. I will say these products are pretty awesome, the ease of putting them in and without spending endless hours i would highly suggest using them where needed. Also little trick to applying them is to wrap some bricks in non-stick to help them stay down.

I wanted to be more safe than sorry and tore out part of the foam for the fish box and put the stiffeners in there as well since its a 40" space between blkheads. I could really tell that the areas that were flexing was where there was just the 2 layers of 1708. While getting the elevation right for the gas tank the beams worked out perfect. The beams glass went to the 2nd layer tab of the stringer glass. On top of that i had some extra 17oz laying around so ended up putting another layer over the 24oz beams, for a total of 41oz.

Surely it should be solid now!

Now to finish the fish box this week and put in bilge paint and get ready to put the floor in, which ive already cut two panels to fit.

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fallguy1000
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Re: 1981 Dolphin 20' Commercial

Post by fallguy1000 »

Okay, I am confused.

You laid them on the hull?

I thought they were going over wide spans above.
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MSRiver
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Re: 1981 Dolphin 20' Commercial

Post by MSRiver »

Fallguy i believe your talking about lateral supports? If you look above those forms i made from the foam board at the outer edges theres pretty much no material once you add the 3/8" neoprene. So it would just be a triangle which wouldnt really tie into anything other than the PVC pipe. Once i found those preformed beams i just opted to do longitudinal sections instead of doing those cross sections. Each cross section moving forward was a different shape, so getting each one just right would be somewhat difficult. This way i could achieve constant contact stern to aft more easily. Also at each section would only be about 16" for it to touch the tank so 4 of those sections is 64" of contact area. The length of contact area running longitudinal is 5' at 3 points of contact that's 180" of contact area. While essentially adding 2 more stringers to the hull.

Maybe to better to explain the points of the hull flexing:

The hull was flexing or making a U shape parallel in the longitudinal direction( between the PVC and Stringer) and was only flexing considerable where it was just the 2 layers of 1708 i put down over the whole hull. While putting transverse pieces to support the hull for the thinner hull glass. I figured i should really build thickness of the hull since areas where there was 3 or more layers of 17 oz like next to the stringers they did not flex at all.

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Re: 1981 Dolphin 20' Commercial

Post by Fuzz »

MSRIVER that looks much better. I think you will be much happier that you took the time to do it. Glue the rubber strips to the tank so it hits the stringers and you should be good.

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Re: 1981 Dolphin 20' Commercial

Post by MSRiver »

This may be a detail I'm overthinking, but the tank doesn't sit flush on the new stringers for the tank. It hits the top outer corners with maybe 1/8" to 3/16" gap on the lower side. To me i was thinking about getting the neoprene stripes installed, wrap in some non-stick put in some thicken epoxy to build up low side and set tank in so that it sits flush on those stringers and not just on the corners.

Thoughts? yes or no

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