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 »

Well spring has brought another cold front so epoxy work got put on hold but got to start playing with the back bulkhead and running chase tubes. Before it did get cold i got to lay 2 layers of 1708 on each side on the back bulkhead as well as finish tabbing strings to the transom, which there was 2 layers of 12oz tape, but after sanding i might have gone a little too deep so added another 2 layers of 1708. I also put 2 9x9 hatches in the back bulkhead for access. I also cut out the stern port cooler box, which really wasnt doing much for me so just decided to cut it out for more access. I didnt want to put one hatch in the middle since im planning on putting a live well in the middle.

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Chase tubes i put 2-3" tubes down the stringers then a 2" on the inside to run wires up front, which i may add another to the other side incase i put a trolling motor up from those power wire will take up a good bit of the 2". On that note i had a good little whoops for the big chase tubes and cut the stringer short of where i wanted them to come up under the console. I know ive seen your not suppose to cut in on the top side of the stringers but with limited room i really didnt have a choice since i cant get another 90° to fit in between the stringer the gas tank. I did make some wood plugs that will fill in those holes. Plan is to lay 2 layers of 1708 to build up thickness, put some epoxy glue in then put 4 layers of 12oz tape over each plug on both sides. Also put in mini bulkheads between the two stringers in front and behind where chase tubes went though.

I also have planned to put in half a 3" pipe down the center to drain water and another 1" to drain specifically the front fish box.

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Fuzz
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Re: 1981 Dolphin 20' Commercial

Post by Fuzz »

Those pvc fitting have pretty tight turns. Most folks use the grey ones for electrical use as they have smoother bends. You might want to try sliding what ever will go in the pvc now to make sure it will work. Much better 5to change it now if you need to.

fallguy1000
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Re: 1981 Dolphin 20' Commercial

Post by fallguy1000 »

Dittos; you can pretend you can make those turns, but they will be cruel real world.
My boat build is here -------->

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MSRiver
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Re: 1981 Dolphin 20' Commercial

Post by MSRiver »

I dont know why that didnt occur to me, but yeah i was looking around here for 3" electrical flexible conduit but those prices blew my mind way. For the 3" 90s i got the long sweeps which is roughly a 8" raduis which was minimum for throttle control bends. Ill look again at the 3" electrical 90s but i saw one and just thought there would be no way Im going to be able to fit it without having to make a long cut in the stringer.

Ideally now that i know this now... the placement of the inner big stringers (which i just put back due to where the original ones were) i should have fit them closer together and spaced them just wide enough to fit the gas tank then i would have a lot more room 1 and 2 I wouldnt have to cut through the stringers to bring them out of the floor under the console. But thats all water under the bridge now.

MSRiver
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Re: 1981 Dolphin 20' Commercial

Post by MSRiver »

Looked into 3" electrical conduit 90°, I just don't have enough below deck space. I would have to cut a 7-9" long hole for it to come out of the sole. I did check running shifter cables and power cables through the long sweep PVC 90° I have now, they work! I will have to remember to not glue the 9" straight piece coming out of the floor so I can fit my hand down there if it snags on the pipe lip.

Since last update, I've glassed in the half 3" drain down the center then the 1" drain that only drains the fish box, if i remember correctly ended up being 6 pieces of 12oz to do them all. Also a little trick for installing the 3" drain, since i didnt want to push epoxy through the gap between pipe and hull and have possible snag areas for junk. I actually sealed all the gaps with hot glue first which helped keep everything in place as well, then just ran my fillets for glass.

Glassed my stringer plugs in with 4 layers of 12oz tape overlapping so each layer has more surface grab. Not worried about sand through there. Turned out pretty good if I say so myself.
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Glassed in two bulkheads for fish box 2 layers of 12oz tape both sides. Which is now 42" long. I had to move the gas tank back to account for the 3/8" neoprene pad to not hit the sole. Also I've got the 2" insulation board for the fish box which was going to cut down inside dimensions. Now i can still obtain 36" inside with the insulation.
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For the gas tank I plan on just running 3 strips of the neoprene that run down each side and one on top of the drain pipes (see picture). I went through and through about making a false floor for it but the amount of time id take to get the angles just right for the tank to sit on would not be time spent well. While doing this will also give more contact area for the tank. Also I was planning on running another bulkhead behind the gas tank that would only house the fuel line that way that fuel line isnt in my livewell bilge area. Unless i should just put the fuel line is a chase tube in the bilge area and not worry about it.
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1. On a side note how are yall preping the neoprene surface for epoxy as well as insulation board?

2. Last year I found a good thread about making plywood hatches not necessarily with drains but had pretty good descriptions and pictures, i cant seem to find it now but seeing if anybody had a good thread to point me to?

3. Just a side comment is it just me or does 12oz tape just have a tendency to not hold epoxy? ie i get done rolling out air bubbles everything looks good then not 10 min later its like the glass picks up and will be air bubbles back in it. Only way ive been somewhat getting around it is i let sit up and get fairly tacky roll out out again and put more epoxy down.

Fuzz
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Re: 1981 Dolphin 20' Commercial

Post by Fuzz »

The neoprene is glued with 5200 to the tank. The idea is to seal the rubber to the tank and not allow water to get between the rubber and the tank. Speaking of the fuel tank I do not like the idea of letting the sharp edges of the tank to rest on the hull. That is a lot of weight and think about the forces involved when dropping off a large wave. It would be much better to spread that force over a larger area.

MSRiver
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Re: 1981 Dolphin 20' Commercial

Post by MSRiver »

I was on the impression from what I've seen its the neoprene mounted to block. Fuzz i see what your say about hard edges without building a complete flood it looks like most people support the tank with essential a bulkhead at the bottom that is roughly 2" wide and run perpendicular to the tank in 3 spots at most. Weight distribution of that is 3 point loads for the width of the tank for my full tank that's 3 places where 118lb rests on the neoprene not more than 2' in length. Now having 3 strips go the length of the gas tank has increased area where now that 118lb is distributed over 6', which is now less lb/ft.

What about insulation for fish boxes? just a light hand sand to roughen up?

MSRiver
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Re: 1981 Dolphin 20' Commercial

Post by MSRiver »

Possible concern which has me pretty worried. I have the whole floor system installed and almost glassed my fish box in. I was stepping around in the gas tank area and the hull is flexing under me not much but noticeable.

Should i add more layers of glass or make wood stringers for the tank to sit on and glass those in with 3 layers of 17 oz like my stringers for support for tank and hull. see picture

Also what about areas such as my fish box and bilge area? Just add more glass?

To add to that, the red lines are the only areas where there is only the 2 layers of 1708 i added to the hull in the beginning.

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Fuzz
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Re: 1981 Dolphin 20' Commercial

Post by Fuzz »

I would want a lot of support for the fuel tank. Think about the forces involved when you have 500lbs of fuel and drop off a wave. Lots of energy concentrated in a small area.
As for the flex in the new stop I would look at small stringers. Glass gets its stiffness from thickness. Adding a couple more layers of glass is not much more thickness.

MSRiver
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Re: 1981 Dolphin 20' Commercial

Post by MSRiver »

Trying to think about the best way to do this, now this is just a cross section of the available room i have to work with, but have not accounted for the 3/8" neoprene pad so i have to take that off as well.

Options:
1. Run 3- 4 cross sections for support? Plan would be round the edges and glass to hull, which they would not tie into anything other than the hull. So they are really just stiffeners

2. Run 2 stringers that tie into the two bulkheads, same method to attach. Now the only problem i see with this, is that the cross sections differ and having that translate to the varying cross section over a long piece.

(The center drain PVC is wrapped with 4 layers of 12oz tape, which should act as a stinger)

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