another 20sf project

[72potter20]

Hey guys, this is my first thread here. this forum has been a wealth of information so far.

A few months ago i decided i needed a project and another boat in the backyard. I found a 1972 20sf in daytona and picked it up and brought it home to st. pete Fl.

it was a bare hull, original trailer, top cap and original center console. the hull had already been completely gutted, the hull sides where reinforced with several layers of 1708 that where layered down and over the outside stringer (guy did a pretty good job imo), the stringers (4 stringer system) had an additional inch of foam glassed to the tops, and the transom was replaced with two layers of 3/4" ply and the notch filled in for a closed transom.

I've been slowly working to complete the project and am at the point where i am going to start putting the deck down. I have shortened the casting platform by about 20" and added a bulkhead between the center stringers, i installed the gas tank up to that bulkhead and glassed in another bulkhead to close off the tank compartment. i then glassed in another about 24" from the transom for a total of 3, all inbetween the center stringers.

i wasnt going to add anymore, but after reading lordwrenches thread i am having second thoughts. it doesnt look like there were ever any in these hulls, should i add more between the other stringers? i wasnt going to reinforce the hull side with more glass, but i was going to add 3 gunnel supports on each side for further reinforcement. I had thought my original plan was overkill, now not so sure. i just dont want to do work twice.

thoughts? I'll post pics soon

[flyingfrizzle]

You may cause hard spots if you add more bulk heads under the deck, the hull needs to flex. I would consider adding some additional glass strips Down the sides of the stringers to the hull bottom. Use 6" or 8" pieces and split the distance half on the stringer and half on the hull bottom. The hull I had, split like his did, it tore the stringer loose from the bottom of the hull. When it did it ripped threw the bottom. A lot of load gets transferred to the hull there. You may even want to add fillets in a radius in the corners then add the strips so it will spread the load.

[dave s]

My Contender has a three piece construction, and the sides of the hull have outside glass, a thin ~1/4" core, which looks like divinycell, and a thin ~1/8" inner liner, which continues onto the sole. You can push on the liner and feel it give slightly.
When you bang on the outside of the hull, it feels a bit flexible, but below the deck line, it's rock solid.
Only two vertical supports to house the fuel lines and wiring, but there are a lot of stiffeners under the cap, which is cored with divinycell foam.
If it was my boat, I'd add some core to the sides, besides the 1708.

[Bushwacker]

On the gunnel supports, are you building a cap from scratch or re-using the old cap? Frizz is right, hard spots at the gussets could be an issue. An alternate approach would be to use a thick core in the cap and make it look like an inverted U, overlapping the hull on the outside and extending down several inches on the inside. The vertical legs of the U create a lot of stiffness and extended all the way down to the deck on the early Moesly CC's. You could get similar stiffness with a shorter and thicker leg, maybe with a rib along the bottom of it. The best way to attach cap to hull would be glass tabbing with epoxy on inside and outside; next best would be to use pop rivets or machine screws; weakest joint would be to use tapping/sheet metal screws with sharp threads that cut the glass fibers and tend to come loose.

If the entire inner liner has been removed, I'd recommend adding balsa core to inside of hull ala billythekid's thread:
http://www.classicseacraft.com/commu...ad.php?t=24262

A tall thin beam/stringer is very stiff in vertical bending but it'll tend to buckle if it's not supported from the side by bulkheads. The original boats didn't need many bulkheads because the cockpit sole was well bonded to tops of the stringers over their entire length, providing significant transverse stiffness. This bond is important, so I'd use epoxy thickened with glass fibers to bond the deck to the top of the stringers, even if poly or vinylester is used everywhere else.

Regarding stringer attachment, I doubt any reinforcement is needed there because the 4-stringer hulls were really well made, with the glass stringers being installed about halfway through the layup. The stringer tabbing is extensive and thoroughly explained in great detail in the Boating Magazine article on the 1969 Seafari 20 in the Literature section. (To get to it click on Classic SeaCraft Home in the blue bar at bottom of page, then click on Literature tab.) I think that is a .jpg file however, so not very readable but I can send you a very clear .pdf version if you PM me with an email address.

If you're planning to install a bracket, I'd suggest you read my Pros & Cons thread at top of this section. Sounds like you're already moving the gas tank forward, but you might also consider moving the console forward some as well. Although the stock 20' hull is extremely stiff, it's relatively light with less beam than modern 20's. This makes for a great ride but it's more sensitive to weight and weight distribution than a heavier fatter hull, so it's good that you're asking questions and paying attention to this stuff before you get too deep into it! Welcome aboard and keep us posted on your restoration! Remember that good pictures are worth a lot of words, plus the guys on this site love boat porn anyway!

[72potter20]

Originally Posted by flyingfrizzle

You may cause hard spots if you do that, the hull needs to flex. I would consider adding some additional glass strips Down the sides of the stringers to the hull bottom. Use 6" or 8" pieces and split the distance half on the stringer and half on the hull bottom. The hull I had, split like his did, it tore the stringer loose from the bottom of the hull. When it did it ripped threw the bottom. A lot of load gets transferred to the hull there. You may even want to add fillets in a radius in the corners then add the strips so it will spread the load.

so these hulls need to flex a little. the outside stringers are bonded very well to the bottom with 1708 from the hull sides layered down and up and over the outside stringer. i will add the tabbing to the two centers. thank you for the response

Originally Posted by Lordwrench

if I understand above the liner is cut and glass is added but not cored?I would look at many pics of different 3 piece boat to see alternatives to strengthen above the deck, the corners of my casting platform which is unmodified are both cracked excessively due to the added loads on that hard point due ot removed liner support. look at the pic of shines 23' I posted, the supports from floor to cap in place of removed liner are key for the above deck rigidity and keeping the loads spread. My boat should have at least three on each side, I also really like the pre-formed "speed bump" shaped ribs he used, I would like to see a boat planned that could only use those slick ribs...One reason being the supports from floor to cap are toe destroyers!!

Where you at in the 'Burg,btw?

B

yes the liner is cut to a "3 piece" design now. several layers of 1708 added to the hull sides and right now there is no coring. to be honest, i was really hoping not to core the sides, which is my reason for adding at least 3 heavy duty gunnel supports from the deck to the cap on each side and heavily glassed to the hull. i do like the "speed bump" idea as well and would prefer to do that before coring.

I'm in the coquina key area, yourself?

Originally Posted by dave s

My Contender has a three piece construction, and the sides of the hull have outside glass, a thin ~1/4" core, which looks like divinycell, and a thin ~1/8" inner liner, which continues onto the sole. You can push on the liner and feel it give slightly.
When you bang on the outside of the hull, it feels a bit flexible, but below the deck line, it's rock solid.
Only two vertical supports to house the fuel lines and wiring, but there are a lot of stiffeners under the cap, which is cored with divinycell foam.
If it was my boat, I'd add some core to the sides, besides the 1708.

thanks for the input. i'll stop by fgci and see what kind of products they have for coring

[72potter20]

Originally Posted by Bushwacker

On the gunnel supports, are you building a cap from scratch or re-using the old cap? Frizz is right, hard spots at the gussets could be an issue. An alternate approach would be to use a thick core in the cap and make it look like an inverted U, overlapping the hull on the outside and extending down several inches on the inside. The vertical legs of the U create a lot of stiffness and extended all the way down to the deck on the early Moesly CC's. You could get similar stiffness with a shorter and thicker leg, maybe with a rib along the bottom of it. The best way to attach cap to hull would be glass tabbing with epoxy on inside and outside; next best would be to use pop rivets or machine screws; weakest joint would be to use tapping/sheet metal screws with sharp threads that cut the glass fibers and tend to come loose.

If the entire inner liner has been removed, I'd recommend adding balsa core to inside of hull ala billythekid's thread:
http://www.classicseacraft.com/commu...ad.php?t=24262

A tall thin beam/stringer is very stiff in vertical bending but it'll tend to buckle if it's not supported from the side by bulkheads. The original boats didn't need many bulkheads because the cockpit sole was well bonded to tops of the stringers over their entire length, providing significant transverse stiffness. This bond is important, so I'd use epoxy thickened with glass fibers to bond the deck to the top of the stringers, even if poly or vinylester is used everywhere else.

Regarding stringer attachment, I doubt any reinforcement is needed there because the 4-stringer hulls were really well made, with the glass stringers being installed about halfway through the layup. The stringer tabbing is extensive and thoroughly explained in great detail in the Boating Magazine article on the 1969 Seafari 20 in the Literature section. (To get to it click on Classic SeaCraft Home in the blue bar at bottom of page, then click on Literature tab.) I think that is a .jpg file however, so not very readable but I can send you a very clear .pdf version if you PM me with an email address.

If you're planning to install a bracket, I'd suggest you read my Pros & Cons thread at top of this section. Sounds like you're already moving the gas tank forward, but you might also consider moving the console forward some as well. Although the stock 20' hull is extremely stiff, it's relatively light with less beam than modern 20's. This makes for a great ride but it's more sensitive to weight and weight distribution than a heavier fatter hull, so it's good that you're asking questions and paying attention to this stuff before you get too deep into it! Welcome aboard and keep us posted on your restoration! Remember that good pictures are worth a lot of words, plus the guys on this site love boat porn anyway!

I am reusing the old cap. when i bought the boat, the cap was already cut into a "3 piece" style. i have restored the cap edge and planned to attach it back to the hull with either rivets or through bolts, no screws. i have boxed in a 16" wide transom area, tabbed to the hull and stringers which acts as hull side aupport as well. the back of the cap will be glassed to the top of this transom box

i had originally planned to bond the deck to the stringers using 5200, not recommended? obviously the sides of the deck will be filled with cabosil and tabbed to the hull sides.

the deck will be marine ply. I was going to use poly resin to glass the bottom, any issues with the thickened epoxy bonding to the poly? would vinylester bond better?

I am planning to do a bracket. ive studied your thread quite extensively. infact i have been stalking this forum for quite some time reading every build thread i can find studying before signing up. the plan is a bracket and an etec 90 or suzuki 90, maybe 115's depending on what i find when the time comes. i'm trying to keep this boat as light and fuel efficient as possible since my grady white is such a gas hog.

[72potter20]

Originally Posted by Bushwacker

Sounds like you're already moving the gas tank forward, but you might also consider moving the console forward some as well.

I like having the raised deck up front, but not as big. One of the reasons I shortened it 20" was to accommodate the gas tank moving forward as far as I could. It's a 50 gallon tank. The console will be moved forward so the seat is 22" from the raised deck, batteries under the console seat.

Anchor will he kept under the raised deck as the forward compartment is to small for a decent anchor Imo. I am thinking of foaming that for flotation instead

[flyingfrizzle]

Originally Posted by Lordwrench

if I understand above the liner is cut and glass is added but not cored?I would look at many pics of different 3 piece boat to see alternatives to strengthen above the deck, the corners of my casting platform which is unmodified are both cracked excessively due to the added loads on that hard point due ot removed liner support. look at the pic of shines 23' I posted, the supports from floor to cap in place of removed liner are key for the above deck rigidity and keeping the loads spread. My boat should have at least three on each side, I also really like the pre-formed "speed bump" shaped ribs he used, I would like to see a boat planned that could only use those slick ribs...One reason being the supports from floor to cap are toe destroyers!!

Where you at in the 'Burg,btw?

B

In my first reply i mentioned the stringer support but forgot to mention what lordwrench was saying. You need to address that too. If hull sides are not cored I would add some vertical sports down the sides or either stiffeners of some sort. I have a master angler hull which is 3 piece from the factory and the hull is twice as thick as the SF hulls. I don't remember vertical stiffeners except the teak rod holders in the sides but there is a horizontal stiffener along the deck. The cap is much stronger than the sf models the way it is boxed in and higher as well. I would do some stiffeners of some type additional to the extra layers they added if you do not core it just to beef up the sides of the hull. My race boat hull is done like this and dose not have any supports and it has stress cracks in the paint right above the deck on the side of the hull all the way down both sides and you can see the sides flex while you run the boat. I will be adding supports to it too.

[72potter20]

This is my solution. I laid in an additional layer of 1808 on the hull sides, then the three gunnel supports on each side with the transom box and forward casting platform bulkhead all glued in place with thickened resin and tabbed with 1808. The boxed gunnel supports will be filled with foam for additional floatation.



The hull feels very solid without the cap being attached yet. The deck is half inch, the forward casting platform will be two layers of half inch for additional rigidity.

[flyingfrizzle]

looking good!