1976 Cobia Tri Hull Transom Destroyed - HELP

[Woodonglass]

Re: 1976 Cobia Tri Hull Transom Destroyed - HELP

Yup, inner skin gotta go!!!!! Top of the transom sides..Gotta go!!!! SawzAll, Grinder, Circular Saw set to depth, whatever it takes, just get it out!!!!! Don't worry about the outer skin being cracked, splintered and full of holes...That can/will all be repaired. Just try and keep it in one piece as best you can. Everything else...Rip it out!!!!!

 

[gilligan2032]

Re: 1976 Cobia Tri Hull Transom Destroyed - HELP

Alright, I'll suit up to do the dirty deed ASAP.

Should I remove all three stringers? Or remove them and replace them one by one?

Also, should I remove the gunwhales?

 

[Woodonglass]

Re: 1976 Cobia Tri Hull Transom Destroyed - HELP

Personally, I think strapping the boat is an excellent way of maintining her shape. Trihulls usually are fairly stable hulls so I think you can remove all the stringers at once If your trailer is a full bunk trailer. If not you could add some additional support underneath as needed. I see no need to remove the gunwales.

 

[gilligan2032]

Re: 1976 Cobia Tri Hull Transom Destroyed - HELP

My weekend was ruined by a druggie trying to break into my detached garage in the middle of the night!!!! Thank God I have two big boxers that alerted me to his presence in the middle of the night, but he had left by the time the cops arrived. I got zero sleep Friday night, and my heart was beating out of my chest!


I did do a little demolition work, and found it to be a puzzle. I used my circle saw set to a shallow depth to cut out as much deck as I could close to the hull. I found it very awkward to use, and seemed dangerous the way I was handling it. I tried out my grinder with a diamond cup wheel that I bought. I had expectations that it was going to chew through material like a weed whacker or something. It definitely is not suited for cutting out large pieces of fiberglass! I was going to use the 36grit fiber discs, but it seems I need a backing pad for them? Should I buy a CUT OFF wheel for the grinder? The instruction manual says I will need a new guard to use a cut off wheel (a type 1 guard). I eventually turned to my dremel tool, which worked really well. Since all the wood is total mush, I am only trying to cut out the fiberglass. The dremel cuts it easily and accurately but it burns through the cutting discs quickly. Would it be worth getting a cheapo oscillating tool at harbour freight? I can imagine that removing the stringers with my dremel could take quite a while.

I kept the fiberglass off well enough! Thanks for the tips...

 

[mercurymang]

Re: 1976 Cobia Tri Hull Transom Destroyed - HELP

If you have a 4 1/2 or 5" grinder, pick up some 24 grit discs along with a pad. It makes quick work of fiberglass. Just be careful as you can eat through your hull if your not paying close attention.

 

[Woodonglass]

Re: 1976 Cobia Tri Hull Transom Destroyed - HELP

The MultiTool cutter from HF does a surprisingly good job of cutting the deck out. The Half Moon blade is a good choice as and additional blade.

 

[gilligan2032]

Re: 1976 Cobia Tri Hull Transom Destroyed - HELP

The MultiTool cutter from HF does a surprisingly good job of cutting the deck out. The Half Moon blade is a good choice as and additional blade.

I would imagine it works great for cutting out the stringers too? (especially considering mine are filled with mushy rotten wood)

 

[Woodonglass]

Re: 1976 Cobia Tri Hull Transom Destroyed - HELP

Yep and a Sawzall with a Long Flexible blade works well on stringers too!!!!

 

[gilligan2032]

Re: 1976 Cobia Tri Hull Transom Destroyed - HELP

I spent the afternoon working.

I started by taking out the rest of the deck using my dremel tool with a diamond cutting disc from harbour freight (only 5 bucks!). It cut as fast as I could move the tool, and had the perfect depth so that I didn't cut through the hull. I found the crowbar useful to pry out the rotted deck wood.

I bought the harbour freight oscillating tool and found it to be very helpful to remove the first stringer. I wish it were more powerful and didn't vibrate in your hand so much! After a while it rattles your bones to death. I burned through the cheapo blades it came with, and bought a Dremel brand blade that seems to last a long time. I also used it to help get the rest of the inner skin removed on the transom. Lots of digging out wood with the crowbar.


LOTS of material removed!

 

[Woodonglass]

Re: 1976 Cobia Tri Hull Transom Destroyed - HELP

Yup, I'd say a pretty good days work!!!

 

[jigngrub]

Re: 1976 Cobia Tri Hull Transom Destroyed - HELP

Your work looks great and you're making some good progress!

 

[friderday]

Re: 1976 Cobia Tri Hull Transom Destroyed - HELP

Good work/progress, indeed. It's so good when you get all that debris out of there & see a relatively clean hull. Now the REAL building begins & it is so rewarding. I wanted to comment on your transom's outer skin. I, too, on my current build, had a transom that both inner & outer skins were compromised...severely. I took out the inner skin & was puckering when I had to cut out about a 6 x 6 area of outer transom after the inner skin was gone. Had a hole I could put my leg thru. I added a couple of layers of 1708 to the inner part of the outer skin BEFORE putting the wood in. It puckered out & I thought, "Oh carp, I'm gonna have a mess". Well, it ain't completely sanded & fared smooth, but very soon, only a couple(hundred) of us will know it was ever there. So, just wanted to offer some encouraging words. I can only guess you might be feeling a little nervous about that, too. Just try to be careful around it, firm it up maybe with a layer or two first, then build yourself a transom. I'll be watching!!
Lisa

 

[gilligan2032]

Re: 1976 Cobia Tri Hull Transom Destroyed - HELP

Thanks for the encouragement! I think I have the rest of the demolition job under control, which is a great feeling. However, despite reading quite a bit, I'm really ignorant when it comes to the building stage. There is so much to learn when it comes to fiberglass, it's daunting! Thank God Woodonglass has that great guide

Where do you guys buy your fiberglass materials? I'm trying to estimate the cost to finish the project. I know it's going to be a lot!

 

[jbcurt00]

Re: 1976 Cobia Tri Hull Transom Destroyed - HELP

us composites

but in nc, you could try composites one. might be able to pick it up & save shipping & hazmat

 

[gilligan2032]

Re: 1976 Cobia Tri Hull Transom Destroyed - HELP

Thanks jbcurt, I remember seeing a pdf materials list someone had for boat restoration that listed how much resin and fiber Is typically needed for a 15 foot boat. Wish I could find that pdf again!

I remember thinking I would need about 10 gallons of resin. Sound right? I have no idea for csm and 1708 :-\

 

[jbcurt00]

Re: 1976 Cobia Tri Hull Transom Destroyed - HELP

That's from WOG, but here's a copy:View attachment Fiberglass repair MaterialsList.pdf

 

[gilligan2032]

Re: 1976 Cobia Tri Hull Transom Destroyed - HELP

It was a demolition day! I got the other two stringers out, and much of the fiberglass tabs ground away. I bought a reciprocating saw from Harbor Freight for 20 bucks that worked wonders for the stringer removal (as you guys suggested- thanks!). I had some fun with my camera and made a time lapse video of the 3.5 hours of work.

I rigged a fan above to help with the dust - worked great!