Stringer and Transom Replacement - I Need Your Help

[MadsBoat]

Well I just joined iboats and this is my first go at this forum.

Recently I purchased a 1973 Sierra Mark IV Cuddy Cabin Boat (I think it was only made from 1973 to 1974 using molds that were bought from another boat company... Maybe dorsett...) After many hours on YouTube I realized that it would be in my best interest to tear everything out and examine the stringers and transom. To make a long story short; the stringers, bulkheads and most likely the transom will have to be replaced. After a lot of time YouTube (special thanks to friscoboater) I have learned a lot about the necessary process to replace the required parts.

The main question that I have is what kind of materials I should use on restoration of a boat of this age? I hear a lot that epoxy resin is the best and not to use anything else. Is this truly the case? What would you guys recommend for putting in new stringers, bulkheads, and of course the transom. Is a polyester resin something that i could use? I want to make this project as economical as possible but I will spend the money to truly do it right at the same time.

I have attached some pictures to show the current state of the stringers. I noticed that there was no foam in there. The guy before me put in a new floor on the old structural members and may have removed the foam. Do I need to put the foam in the floor? I suppose it couldn't hurt and will only make for a stronger hull....

All the advice I can get would be greatly appreciated.

 

[StevenT]

Re: Stringer and Transom Replacement - I Need Your Help

Nice Boat. You can plan on polyester resin. Epoxy is to expensive from a manufactures profit margin. There are some very knowledgeable and helpful guys here. You can get plenty of help here.

 

[tpenfield]

Re: Stringer and Transom Replacement - I Need Your Help

Welcome to iBoats . . .

You could use Vinyl Ester resin as compromise between polyester resin and epoxy. VE will be a little bit more money than poly and have some of the benefits of epoxy, such as better water resistance and adhesion.

as far as a core material for the structure, if you are going to use wood, you can use sheathing rated exterior plywood. As far as foam - yes add the foam, using the 2-part polyurethane foam. Read up on the instructions for working with the foam, and there are also some YouTube videos of using as well.

post some pictures as you go, we like to see the progress.

 

[Georgesalmon]

Re: Stringer and Transom Replacement - I Need Your Help

You have a 40 year old boat that has rotten wood. It was made with polyester resin and the fiberglass is OK right? Hull still in one piece? Why would you want to use more expensive resin to repair it? Do it properly and there's a lot of help in this forum and you'll be happy for another 40 years. Save your money for other stuff thats more important and just use polyester IMHO.

 

[Woodonglass]

Re: Stringer and Transom Replacement - I Need Your Help

She's Made from Poly so I'd stick with it. The first link in my signature has some helpful info.

 

[jigngrub]

Re: Stringer and Transom Replacement - I Need Your Help

Use the better quality fir ABX or BCX grade plywood sheathing, fir is less likely to warp and the voids will be smaller in the better grades of plywood. Make sure you use the X exterior grade plywood.

Don't be suckered in by the pretty faces of the birch, maple, and cherry hardwood veneer plywoods. These are cabinet grade plywoods and for indoor use only.

Avoid pressure treated plywood, pressure treated wood isn't kiln dried and has a very high moisture content that will prevent you resin from bonding and curing properly.

 

[a1964rn]

Re: Stringer and Transom Replacement - I Need Your Help

If you want to use the cheapest, use polyester. If you want to use the best, use epoxy. Epoxy has a much higher secondary adhesion strength than polyester. Epoxy also has no harmful fumes/vapors and is not flammable. Not to mention the increased moisture resistance of epoxy.
It's your boat, your choice, just do your research and educate yourself about each one before making your decision.
Good Luck and welcome to iboats!

 

[MadsBoat]

Re: Stringer and Transom Replacement - I Need Your Help

Thanks everyone for your help thus far! I truly appreciate your willingness to share what you know... I plan to post pictures during the entire restoration which started as just a few minor repairs and has developed into the desire to make a Newish Boat... I now think i will replace the entire interior, all the gauges, all the wiring, the rub rails, and see what kind or rebuild / servicing the sterndrive needs.

A couple quick questions:

Any recommendations on manufacturere / suppliers for the resin and fiberglass material (polyester, vinylester, epoxy)?
I have heard of a place called US Composites... I think?

I want to estimate so that i have extra material and not less. For me to put two new stringers (about 12' long) and completely redo the transom and seal both sides of the new plywood floor; how much resin are we talkin. This would include enough for me to make "peanutbutter" for the fillets and apply several layers to the transom and stringers. It would be nice to know what you guys have found as maybe a general rule for coverage...

 

[Woodonglass]

Re: Stringer and Transom Replacement - I Need Your Help

U.S. Composites, Inc. - Fiberglass , Epoxy , Composites, Carbon Fiber.
15 yds of 1708 biaxial cloth
20 yds of 1.5 oz Chopped Strand Mat (CSM)
15 - 20 gallons of 435 resin Resin
4 gallons of Cabosil
1 lb 1/4' Chopped Milled Fibers

 

[MadsBoat]

Re: Stringer and Transom Replacement - I Need Your Help

U.S. Composites, Inc. - Fiberglass , Epoxy , Composites, Carbon Fiber.
15 yds of 1708 biaxial cloth
20 yds of 1.5 oz Chopped Strand Mat (CSM)
15 - 20 gallons of 435 resin Resin
4 gallons of Cabosil
1 lb 1/4' Chopped Milled Fibers

Thanks Woodonglass for your quick responses!

Here is the next set of questions and a few pictures to go along with them:

I have cut into the stringers to see how bad they really are. What I have found is the wood seems to be pretty good but the glass seems to want to separate a little bit. I imagine there is a little moisture contributing to the problem. Notice in my pictures that the outer part of the sample that I removed is darker probably due to some moisture infiltration at some point during its life. I plan to redo the stringers regardless of the level of rot at this point. Also notice that a 2x4 was screwed to the stringer down by the engine. In that same area you cam see the wood at the bilge that I drilled several holes in. Absolutely rotted (very soft and saturated).

What kind of wood do you guys recommend for the replacement stringers? The wood I removed looks like pine / fir but I am not certain.

I plan to use exterior grade plywood for the bulkheads and decking and maybe marine grade for the transom. Any comments on that??

I plan to leave the top of the boat intact to maintain the shape of the hull a little better and also remove the engine of course. Can I expect the boat to truly maintain its proper shape while it is stripped of all its structural support? I built a cradle for the boat to sit on while I do all this work and I modeled the trailer pretty closely to maintain shape. Any other ideas I should consider like doing one stringer completely before removing the next?.

I am in Utah enjoying the cold. I have the boat in a garage but I don't think it will be much above 50 degrees for me to work. I will go to the expense of a heater if I need to. Will PL glue be ok if I have the patience to let it cure in the cold? How about peanutbutter in this temp? I will be patient and wait for rising temps but that will probably mean that I won't enjoy the boat this upcoming season... And that will be torture!!!

I plan to use the polyester resin at this point for the boat.... The catalyst that it comes with is the only thing I need for a full cure right???

 

[Georgesalmon]

Re: Stringer and Transom Replacement - I Need Your Help

All you need for full cure is MEKP which is the cat that comes with the resin. And you need higher temps than 50 F. Best is about 70 for proper results but high 60's will work sort of OK. The resin will get hard but won't get full cure for a long time at lower temps. Most people support the hull because it will move when all the stringers are reoved. The best wood has already been mentioned, exterior grade plywood 3/4" doubled to replicate the lumber curently in there. Good dry pine or fir 2 x will work too and was used in many boats. Get everything ready,wait for warmer would be my choice. IMHO

 

[73Chrysler105]

Re: Stringer and Transom Replacement - I Need Your Help

I would get a heater you can pick one up from Northern Tool for fairly inexpensive under $50 possibly two if you catch them on sale. For cost savings use the poly just realize you can not use any flame heaters with it. Also you will need to be able to vent the fumes out of the garage so they don't end up in the house.

 

[JASinIL2006]

Re: Stringer and Transom Replacement - I Need Your Help

I have an unheated garage that I'm using as a workshop for my transom/deck rebuild. I have an electric radiator-style heater that I use to keep the temps from getting too low the night before I plan to do some work. Then, the day of boat work, I have two propane heaters (little things that mount on top of the same 20 lb. tanks you might use on a barbecue grill) that I fire up early i the morning. By afternoon, on a day where outside temps are in the 20s or 30s, I can get the garage temp up into the mid- to upper-sixties. On warmer days, I can get into the 70s in the garage. This has worked fine for glassing (I'm using poly resin) and peanut buttering. I would never use PL in this setup, because it takes at least 72 hours to cure, and it would be difficult/expensive to keep the garage temps up that long.

I was also worried about glassing with poly resin around open flames, but I read up on it, and it sounds like, unless you're really doing a lot of glassing (e.g., spraying with a chopper gun), there aren't enough volatiles in the resin to cause problems. I am VERY careful with the MEKP and with any acetone - for example, I would never use any but the smallest amount acetone around a flame; in those instances, I wait for a warm day and either pull the boat outside or open the door. I'm getting close to the point where I'll be glassing my deck, and I'm not sure I'll be doing that with heaters running.

The stuff really is stinky, though, so if your garage is part of your house, you might want to consider whether you want to stink up the house. My wife and kids complain about the smell just from my clothes when I come in from glassing. I can't imagine how it would smell if my garage was adjoining the house.

Jim

 

[ezmobee]

Re: Stringer and Transom Replacement - I Need Your Help

If you have a 240V outlet in your garage (or your fuse panel is out there because it's real easy to add one) get one of these DAYTON Electric Space Htr, Fan Forced, 208/240V - Portable Electric Heaters - 3VU34|3VU34 - Grainger Industrial Supply I got one for my restore to cure the epoxy and it worked great. It's been handy to have a couple of other times as well. It heats my 2 car mostly uninsulated garage fine.