16' Fiberglass Tri-hull Rebuild

[SAT_Bob]

Greeting, I have an old tri-hull runabout that was given to me by my uncle a few years ago and finally decided to get it running. The outboard is a 60hp Suzuki and runs great.

My son and I took it to the lake for a test drive and to do some fishing. All was going well for the first several hours and then I began noticing some water in the boat. It didn't seem like a lot but I wasn't sure where it was coming from. About an hour later I realized there was a lot of water. The boat didn't have a bilge pump so I bailed some of the water out but didn't know where it was coming from. Finally my son noticed a crack in the transom and we saw the water coming in pretty fast. I headed to the boat ramp while my son was bailing. We got it out of the water and saw the extent of the damage. Two large tears in the transom at the bottom of the motor mount.

I found this site after looking around for some options - at first thinking maybe I'd need to just chunk the boat. You guys have given me the confidence that I can do this and wind up with a much better boat. I plan on fishing from the boat most of the time, primarily bass, so I'd like to set it up with that in mind. Not sure exactly what that will entail at this time but I've got some ideas and will be working them out as the project progresses - I'm a long way off right now.

Well anyway, here's what I have a 16' 1973 tri-hull runabout with a 1983 60hp Suzuki outboard. It's a National built by Scottie-Craft. I haven't been able to find out much about the boat but I don't belive they're still in business or that they even made very many boats. If you have any info you can share that would be great.

Thanks in advance for the help as I work through this. Here are a few pictures of the boat before we started the project.

 

[SAT_Bob]

Re: 16' Fiberglass Tri-hull Rebuild

We've taken the boat apart of make all necessary repairs. Removed the rub rail and all the rivets to remove the cap which is now in the back yard. We removed the front seating area and it's in the back yard. We removed the floor to check on the stringers figuring they would be rotted on a 40 year old boat. While cutting out the floor we cut a hole in the hull with the circular saw. A pretty long hole actually. More on this in the pictures below. I'm in the process of removing the old wood from the transom now. The center stringer is visibly rotted at both the bow and stern sides but the middle seams to be okay.


My son headed back to college so now I'm on my own on the project. Oh yeah, and you guys. I'm really glad I had his help with a lot of the heavy lifting and hard work.


So here's where I'm at now.

• Continue removing old transom wood and sand/grind down to the fiberglass.
• After all wood is removed from the transom I'll need to cut out and patch where the transom is torn. I saw this video for patching fiberglass and plan to use this method. Basically, two pieces of 1.5oz mat followed by alternating layers of 9oz cloth until the thickness is the same as the original. I'm also planning on using polyester resin. Will this work?
• Patch the hole in the transom caused by the circular saw. Will do this the same way I patch the transom, I just won't need to cut anything out first.
• Remove the center stringer.
• Should I test the two side stringers to verify they're okay by drilling a few small holes and checking the wood? If so, what's the best way to patch the holes?
• Build and glass in the new transom and stringer(s).
• When I glass in the transom and stringers I plan on using two layers of biaxial/1708. Will this be okay?

I'd also like to paint the boat so I'll be checking back on that later but plan on using the Roll n' Roll method outlined by Woodonglass.

Here are the cracks in the transom.




Everything out but the stringers and some of the transom wood. I do have it on the trailer right now but have stands under the chines where the trailer doesn't really support it too much. I also have two braces, one towards the bow and the other towards the stearn holding the sides up so it doesn't sag.




One exciting thing that happened while removing the floor is my son cut through the hull with the circular saw. I set the depth and he did the cutting so we're both in on this. It's a pretty long cut about 5 feet. So that will give me some additonal fiberglass work, um experience. Also, in this picture you can see one of the stands on the port side at the stern. The boat is about an inch or two off the trailer.




Here's some of the wood we pulled from the transom.

 

[SAT_Bob]

Re: 16' Fiberglass Tri-hull Rebuild

And a few more pictures:

Here's a picture of the boat on the stands while we were working on it in the drive way. The trailer is under the boat but it's lifted up and completely on the six stands.

Here's a picture of the boat on the stands while we were working on it in the drive way. The trailer is under the boat but it's lifted up and completely on the six stands. You can also see the braces I made to support the sides.







We built this stand for the outboard based on the design by dh4winn79 using some lumber we had laying around. I just needed to buy the casters and screws. Very good and easy to follow design. The motor is actually running in this picture.






Here's a picture of the front seating area sitting in my back yard.

 

[SAT_Bob]

Re: 16' Fiberglass Tri-hull Rebuild

Here are some thoughts on the next several steps I need to take:

1. Continue removing old transom wood and sanding down to the fiberglass.

2. Repair the torn transom following this video (How to Repair Fiberglass - YouTube)

• Cut out area where the transom is torn.
• Grind down the radius that I cut out to create the scarf. I bought a RO Sander to use to hopefully cut down on the dust since I can hook it up to a shop vac.
• Clean with Acetone
• Create a backing on the outside of the transom to main act as a mold using wax paper and somthing stiff such as a flexable cutting board or thin plywood that can be taped and held in place as tightly as possible.
• Instead of a first layer of gel coat I plan on using the resin since I'll be painting the boat at some point.
• Apply two two pieces of 1.5 oz mat
• Apply a layer of 9oz cloth
• Alternate layers of 1.5oz mat and 9oz cloth until the thickness is the same as the original.

Notes:

• Each layer of glass will be about an inch larger in diameter than the last.
• Also, I'm planning on using polyester resin since from everything I've read here, that's what the boat was originally built with.
• I'll also be using a respirator, eye protection and a hooded Tyvek jumpsuit.

3. Patch the hole in the transom caused by the circular saw. I'll do this the same way I patch the transom, I just won't need to cut anything out first, since that's already been done.

4. Remove the center stringer keeping as much as I can intact to use as a template.

5. The two side stringers appear to be okay but should I verify this by drilling a few small holes and checking the wood? If so, what's the best way to patch the holes?

6. Build and glass in the new transom.

• Use two pieces of 3/4" exterior grade plywood glued together.
• Cover all sides of new transom with poly resin to seal.
• Glass in the new transom with a layer of 9oz cloth.
• Glass the outside of the new transom to the hull using two layers of biaxial/1708.

7. Build and glass in the new stringer(s).

• Not sure what type of wood to use here so I'm open to suggestions but I'm thinking a 2x6 or 2x8. I'll need to double check the depth to verify.
• Glass the new stringer to the hull using two layers of biaxial/1708.

8. Build the new floor. My planned steps will follow in another post since I'm sure they'll change based on your responses to these steps.

9. Remaining build out to complete the boat... More to follow...

 

[SAT_Bob]

Re: 16' Fiberglass Tri-hull Rebuild

On thing I forgot to mention, if there's anything I should do differently or you have anything else I should consider please let me know.

 

[jigngrub]

Re: 16' Fiberglass Tri-hull Rebuild

... and people wonder if it's ok to run their boat with a rotten transom.

Glad you made it back to the dock before taking on too much water and losing your boat to the bottom.

The state of your boat in decay is pretty typical, as well as the transom damage and the mistakes with the circular saw.


It sounds like you have a pretty good handle on what needs to be done for fix on your boat. The polyester resin will be suitable for your needs.

I'd remove the 2 "flat" stringers wether they needed it or not just so eveything in the boat was new again. It's not that much more work and since you're already there it would be much easier than having to come back later and do it.

You may want to consider an angle grinder with the round rubber backer and 24 grit discs for grinding the inside of the hull and transom. Yes it'll throw some dust, but the speed at which you'll be able to work and the short time it'll take to do the job will be worth it.

If you go with dimensional lumber for your stringers, try to find Douglas Fir instead of regular pine.
Use a good grade of exterior grade plywood for your transom, ABX or BCX... CDX shouldn't be a consideration.

For the patches on you hull and transom cuts I suggest a bigger lap than 1" at a time, more like 3" all the way around. You'll want the patch to be a good 18"-24" wide when you're finished for strength.

 

[Woodonglass]

Re: 16' Fiberglass Tri-hull Rebuild

You might want to take a look at this..."Fabricating Decks, Stringers, and Transoms"

 

[SAT_Bob]

Re: 16' Fiberglass Tri-hull Rebuild

Hey guys, a couple of questions. I was planning on using 9 or 10 oz cloth along with 1.5 oz mat to repair the hole in the transom and where the circular saw got away from us but locally I can only find 6 oz cloth. Will 6 oz be okay? Will it just require more layers?

Another thing is when looking at some of the sites they have E Glass, S Glass and even Boat fabric at Fiberglass Supply. Does this make a difference?

When I glass in the new transom and stringers I'm still planning on using the 1708 because that's what most seem to use. My question here though is the 1708 better to use since it's stronger or that it requires fewer layers than the same thickness required with 1.5 mat and 6 oz cloth? Not even sure this question makes sense. I'm still very new to fiberglass and the different types.

Also, i have a question about patching the holes. I know I need to grind a scarf along the edge of the hold following 12 to 1 rule. But what about filling in the hole? I was planning on starting with two pieces of mat a little larger than the hole and then each subsequent layer of cloth/mat will be larger than the previous. But then some of the things I've read makes it sound like the first two layers of mat need to be the largest and then each subsequent piece is smaller than the previous. Which is right? smallest to largest or largest to smallest? I'm going to grind the scarf from the inside since I have total access to the hull.

Thanks a lot for your help.
Bob

 

[Woodonglass]

Re: 16' Fiberglass Tri-hull Rebuild

Cut out all the damaged glass. Don't worry about fixing em now. No sanding or grinding required. The repair will be done during and after the transom has been installed. You only need 1.5 oz CSM and 1708 Biaxial Fabric for all of your repairs. USComposites is a good online resource for this. Where are you located? Just get the inside of the transom skin sanded and ready for the new transom to be installed. Once it's ready and the new wood transom is fabricated and ready for installation we can go over how to get the holes ready for repair. It's quite simple and easy to do actually. The Cut in the hull just means you're an official iBoats Restorer now!!!!:lol: It's an easy fix to. Since you'll be painting these repairs will totally disappear when you're done.

 

[SAT_Bob]

Re: 16' Fiberglass Tri-hull Rebuild

Thanks for the reply. I'm in San Antonio, Tx. For now then I'll just get the remaining wood off the transom skin and get the new transom cut and ready to go. I'll let you know. Funny about the cut, I didn't feel official when it happened but I'm glad I'm not the only one.

 

[SAT_Bob]

Re: 16' Fiberglass Tri-hull Rebuild

Well it's been slow going lately but I have been able to sand/grind on the old transom some to start getting it cleaned off. Quick question, about how thick should the outer transom skin be? It's a 16' tri-hull with a 60hp. I know the completed transom will be just over 1.5" but as I sand it just seems like the fiberglass is really thin. I'm only sanding until I see glass so I don't think I'm taking off too much.

 

[jbcurt00]

Re: 16' Fiberglass Tri-hull Rebuild

The port side of the transom looks to be just about right, ground to good glass.

You'll use a poly resin filler to adhere the transom ply to that outer fiberglass skin, and after tabbing a couple full layers of glass over the transom & out onto the hull sides, plenty of glass to support a 60hp OB & keep it all working as it should: Keeping the wet side wet & the dry side dry...

Check the details @WOG's signature link:
"Fabricating Decks, Stringers, and Transoms"

 

[SAT_Bob]

Re: 16' Fiberglass Tri-hull Rebuild

Okay, thanks for the info.

 

[Woodonglass]

Re: 16' Fiberglass Tri-hull Rebuild

What do you mean by "Really Thin". Is it less than 1/8"???

 

[SAT_Bob]

Re: 16' Fiberglass Tri-hull Rebuild

Right at 1/8" but some spots thinner. Should I add an extra layer of 1708 before putting in the new transom to be safe?

 

[Woodonglass]

Re: 16' Fiberglass Tri-hull Rebuild

Nah, you'll be using a bunch of thickened resin (Peanut Butter) to install the new transom and that will be adequate to beef it up. 1/8" is pretty common. When you're done it'll be a tank.

 

[SAT_Bob]

Re: 16' Fiberglass Tri-hull Rebuild

Sounds good. Thanks...

 

[ondarvr]

Re: 16' Fiberglass Tri-hull Rebuild

You asked about using cloth, in most applications like this cloth is almost useless, I could go into detail, but just know that it's not needed. The 1708 will work well, and 24 oz roving works too, just a little old school, but much better than cloth.

 

[SAT_Bob]

Re: 16' Fiberglass Tri-hull Rebuild

Thanks for the info ondarvr.

 

[SAT_Bob]

Re: 16' Fiberglass Tri-hull Rebuild

Greetings, I'm going to be placing an order in the next few days from U.S. Composites for some of the materials to get started with the repairs.

Here's what I have on the list:

• 1.5 oz CSM,
• 1708 Biaxial,
• Polyester Resin, I?m ordering from U.S. Composites and they have 435 Standard Polyester Layup Resin (Marine Grade Resin). Based on the name this sounds like the right stuff. Let me know if I need something else.
• Do I need to buy Surfacing Wax for the final coat?
• Fiberglass Detail Roller. They come in a variety of sizes, what is a general purpose size I should get? Roller sizes vary from ?? to 1? and the roller length from 1? to 7?.
• Is a corner roller needed or can I just push the fiberglass into the corners with my fingers?

Does this sound right?

I'm planning on getting the gloves, mixing containers and brushes from HD or Lowe's.