Sunseeker 21’ Rebuild

[Sunseeker26]

Hello!

I have recently purchased a Sunseeker Sports 21’ According to the seller it’s a 1985 but I contacted Sunseeker directly and they have said it was a model built between 1977 and 1980.

Anyway, I plan on restoring her but also adding a few modern touches along the way. My first large job was to remove the carpet, plywood subfloor and remove the original fuel tank. (She would of originally had an inboard motor but it’s been professionally converted to have an outboard motor) The original fuel tank was all disconnected and now is just dead weight.

Unfortunately it seems that most of the stringers are rotten. I’ve read on multiple forums and articles that you should replace like for like. Same active core, same glass etc… But the tops of the stringers haven’t been glassed over like I have seen on stringer replacements on other boats. Is this okay? It also looks like the original glass is quite thin.

I’m replacing the Stringers with 12mm Marine Ply as this is what is currently in place. I’m a little stuck on which fibreglass to use and how many layers.

Any help or advice would be greatly appreciated!

 

[Chris1956]

I like to use dry pressure treated dimensional lumber for stringers. If plywood gets wet, it fails very quickly. PT solid lumber will last for years if it gets wet. After the stringers are installed, foam up the cavities for hull strength and floatation.

If you want a built-in fuel tank, it must be sealed and have a sealed connection to thru-hull vent and fill fittings.

Finally deck the floor by placing resin-saturated strips of cloth or mat on the top edges of the stringers and frames. Now screw thru the plywood into the stringers. Finally, cover the plywood with 2 layers of light cloth or 1 layer of heavy duty cloth and saturate and fill the mesh with resin.

 

[MikeSchinlaub]

I prefer you marine ply plan. Polyester resin, 1.5oz chopped strand mat, woven roving (I don't remember the weight), and a thickener for the resin.

Bed the stringers in the thickened resin, 2 mat and 1 roving on each side with 6 to 8 inch out on the hull. If you want to cap the stringers with glass, cut seperate strips. Glass won't roll around corners. Plan on doing the transom too.

Tyvek suit, disposable gloves, full face respirator, P100 filters, organic vapor filters, fiberglass roller, chip brushes, acetone.

 

[Chris1956]

Mike, so you think screws into the end of 12mm plywood will hold well, or are you not using screws to hold the plywood deck in place? Just curious.

 

[Chris1956]

Also, light FG cloth will bend around corners. Even medium cloth will bend, Using SS staples to hold it in place until the resin cures, can be useful.

 

[Sunseeker26]

Thank you both!

I’m going to stick with the Ply as it is what Sunseeker used. So Polyester Resin is okay to use? I priced up the job using West Systems Epoxy and it’s a lot more expensive.

I read somewhere that polyester resin is stiffer and doesn’t do as well with stress??

 

[Sunseeker26]

@

I prefer you marine ply plan. Polyester resin, 1.5oz chopped strand mat, woven roving (I don't remember the weight), and a thickener for the resin.

Bed the stringers in the thickened resin, 2 mat and 1 roving on each side with 6 to 8 inch out on the hull. If you want to cap the stringers with glass, cut seperate strips. Glass won't roll around corners. Plan on doing the transom too.

Tyvek suit, disposable gloves, full face respirator, P100 filters, organic vapor filters, fiberglass roller, chip brushes, acetone.

Would these work..

- ECF Polyester Resin
- 450G (1.5 OZ) CHOPPED STRAND MATTING - 965MM WIDE
- 600G BIAXIAL CLOTH - 1.27 MT WIDE + - 45°

I don’t plan on capping the stringers as it wasn’t done from factory, I keep reading that you should replicate the existing rather than improve/change.

 

[MikeSchinlaub]

Also, light FG cloth will bend around corners.

I misspoke on that. It will bend, but it will cause air pockets at the

So Polyester Resin is okay to use?

That's what the boat was made with. Also, csm is bonded together with an adhesive that is broken down by the poly resin, but not by epoxy. So epoxy shouldn't be used with csm.

I read somewhere that polyester resin is stiffer and doesn’t do as well with stress??

I'm not really knowledgeable on the chemestry and physical properties of the stuff, but hulls made back in the '70s are still around. The wood is the weakest link. Some people will rebuild everything with coosa, but that's like $400 for a 4x8 sheet. Maybe more now and depending on thickness.

Mike, so you think screws into the end of 12mm plywood will hold well, or are you not using screws to hold the plywood deck in place? Just curious.

We use drywall screws. Stainless is overkill. If moisture can get to the screw to cause rust, then it will rot the wood anyway. Also another 2 mat and roving around the edge of the floor. It's structural, tying the hull to the floor.

I keep reading that you should replicate the existing rather than improve/change.

Same concept as a car really. There's no one right way, and three people will have three (or four) opinions on the same thing.

 

[airshot]

Far cheaper to buy the boat you really want without all this work. Good Luck!

 

[Sunseeker26]

Thank you Mike, I appreciate all your insight.

@airshot, I didn’t realise the stringers were in this condition unfortunately, the floor felt sturdy and sound!

The work actually excites me, I’m a perfectionist and I’m really looking forward to putting a stamp on this boat. The different types of glass and resins is a bit of a minefield but excited to learn it!! Unfortunately here in the UK most used boats are fishing ones that are more suited to our waters, I wanted a cruiser that can both!

Bust Out Another Thousand

 

[Sunseeker26]

She will be a fantastic boat once her bones are restored! A lot of the original features are there so she’s worth it!

 

[Chris1956]

There is nothing like sheetrock screws driven into 12mm plywood edge to inspire confidence in your rebuild. Will they pull out or rust out first?

 

[Pmt133]

The bond of the deck to the stringers really should be the chemical bond of whatever adhesion method you are putting between them. The screws are just holding it until it drys imo and really aren't that important after the fact.

My 4winns had no chemical bond to the stringers. Just steel staples driven through the tops of the uncapped stringers and a crap ton of CSM on the deck top to hold it in place. If you sealit right the drywall screws will outcast you probably. That being said, I used and recommend 316 hardware.

 

[Chris1956]

The plywood keel of my 18' SeaRay was stapled to the bottom of the skiwell. After some time the staples rusted away, the plywood keel fell over and the hull deformed. Since the keel was under the waterproof floor of the ski well, this should have never happened, but it did.

Use Stainless steel hardware. It is a few cents more and you don't need to worry about it. Remember every time you drive a screw thru the deck to mount a seat or something, water can find it's way into the structure. Heck, water can usually find a way past the best waterproofing.

Also, mechanical fasteners are pretty important as they fail less catastrophically than resin-glued joints. Used together they add lots of strength.

 

[Pmt133]

The plywood keel of my 18' SeaRay was stapled to the bottom of the skiwell. After some time the staples rusted away, the plywood keel fell over and the hull deformed. Since the keel was under the waterproof floor of the ski well, this should have never happened, but it did.

Use Stainless steel hardware. It is a few cents more and you don't need to worry about it. Remember every time you drive a screw thru the deck to mount a seat or something, water can find it's way into the structure. Heck, water can usually find a way past the best waterproofing.

Also, mechanical fasteners are pretty important as they fail less catastrophically than resin-glued joints. Used together they add lots of strength.

I agree with everything you wrote. I just worry about how well a wood screw will bite into the grain end of half inch ply. If it were 3/4 I would be more comfortable but you don't get a ton of wiggle on half. I cleated my stringers with nailers for the deck so I had 2 inches of structure every way. This would go back to using dimensional lumber on the stringers and would accomplish the same as that, just with 1 less step...

For seats and everything, I glassed seperate nailers on top of the already glassed deck. There are no screws into deck or structure so theoretically I never should have to worry.

The good thing is if it lasts half as long as the original, I'll be retired and able to do it all over.

 

[Chris1956]

I am also concerned about screws into the ends of 12mm plywood. It has to bite and hold onto veneers of wood.

Plywood is likely cheaper than solid lumber, which is maybe why the boat builders use it. It is also strong enough if it is intact, but that is the issue.

I doubt SeaRay expected water to infiltrate to the keel, but it did, under normal use. The plywood keel SeaRay used was mush. I replaced it with solid PT lumber and SS screws, and rebuilt the ski well with dry PT plywood and some PT 2X2 nailers for strength. I did not think a plywood box w/o reinforced corners was a good idea, even if it was cloth and resin covered.

My SeaRay was about 10 years old when the keel failure occurred.

 

[Pmt133]

Cost probably and that it really doesn't need to be as strong with all the glass on it. Figure if they're using how many sheets for the deck core it's probably more cost... cheaper to use one more sheet for the stringer core.

I'd guess dimensional alone is probably strong enough for most hulls and ply plus glass is probably still weaker. Only draw back with Dimensional is it'll elongate more with temperature swings so maybe it'll debond in some applications? I don't know.

My 4 winns used dimensional for the outside deck supports... I can't call them stringers as they were glassed barely on one side and didn't look structural. They were replaced with 3/4 ply properly bedded and tabbed as stringers. And the second area was the real support under the fuel tank. That was rotted to all hell and mush. That was replaced with 3/4 ply as well. Reason... I had exposure exterior ply left over.

 

[redneck joe]

do not stick with plywood just because its what was in there.

Lots of changes and learnings and such since the 80s

The 80's gave us Ford Pintos with gas tanks in the ass end and chevy trucks with side saddle tanks. They dont do that anymore.

 

[MikeSchinlaub]

I've worked on both dimensional and oly structure boats. They both end up rotting, but both last a long time. Good ply can be stronger than dimensional because the grain goes both ways, and can handle stress in multiple directions better.

I didn't convert mm into freedom inches, so I didn't think of the thickness there. I still think the drywall screws are fine. Once the floor is all glassed in, they aren't really that critical anymore, especially if the floor was bedded onto the stringers with something.