Replacing transom from outside

[oldtwainer]

I have a 1979 17'Mark Twain O/B that the transom is bad around the motor mount area and extends out about 8 inches away from there in all directions. I found this out during my last outing with this boat when tuning up the engine and under a hard acceleration it cracked the exterior gelcoat around the engine mount. This is one of 3 Twains I own and I am planning to give this one to my daughter so I want to be safe. My question is what are the pros and cons on replacing the entire transom from the outside leaving the cap in place or would it be better to remove the cap and replace it from the inside. Thanks for the help

 

[gspig]

Re: Replacing transom from outside

If you remove the outside and the transom wood, what will hold the shape of your hull?

 

[JasonJ]

Re: Replacing transom from outside

Do the extra work and replace the transom from the inside. Cutting the hull shell from the outside weakens the hull no matter how you rebuild it or what you rebuild it out of. I don't care if you use NASA grade epoxy, that hull will not be as strong once that shell is cut. You need the integrity of the hull shell, otherwise you are giving your daughter a boat that can be unsafe. Good luck

 

[Mark42]

Re: Replacing transom from outside

I don't understand why the boat is weakened by removing the transom outside skin. If a new transom core is epoxied in place and the skin is epoxied on and the seams tapered and glassed over it should be as strong as new. I've read where the major load on the transom is forward from the o/b pushing. So if the inside skin is not damaged, and the new core installed properly, then the outside is not really supporting any stress. Am I way off here?

 

[JasonJ]

Re: Replacing transom from outside

I am not going to say you are way off base. What I will say is the original hull shell was formed as a singe layup. Even with the best epoxies, you are not going to get as strong as the original layup when you cut that outer shell and then re-glass it. The inner skin of the transom isn't nearly as thick as that outer shell. It is more to hold the transom wood in and attempt to seal it. Transom loads are not always linear. You have twisting and flexing, all of which is different depending on if the boat is under throttle in a tight turn, or pushing through heavy chop, or trying to pull a heavy water skier. It just is not worth the risk to cut that outer shell when you can either pull the top or at least cut the splashwell and redo the transom that way. Do not underestimate how much force that hull shell sees.<br /><br />I do know that people have done transom jobs as you describe, and they have worked, but I have never been able to know if the transom ever failed. Its the sort of data that is hard to locate because people get rid of boats often, or just junk them. <br /><br />I just think it is a bad idea, and I am not the only one who thinks this way.

 

[epresutti]

Re: Replacing transom from outside

Guys,<br /><br />I have rebuilt my transom by cutting the outter shell. When I read up on replacing the transom, either method, inside or outside was an acceptable repair.<br /><br />There are lots of repairs of this type made, especially when the outer shell is what is cracked. You must make sure that the inner shell is in tact. On my boat design (Mitchcraft) there was not an inner "shell", the transom was sprayed into the mold. I reenforced the inner "shell" as part of the repair.<br /><br />My decision was based on the fact I had not intended to replace the transom and had already replaced the stringers and glassed everything in. I used double bias stitched matt and created another inner hull that wrapped around the inside of the transom approx 6" to the sides.<br /><br />The biggest issue was making sure if you are cutting the outside of the shell is that you leave at least a 4" perimiter and when you reglass you overlap the perimiter. It was recommended to me that for this type or repair it is recommended that you use epoxy.<br /><br />Further you must make sure when you fit the new transom "in the slot" there are no gaps between the new wood and the hull shell. I laminated several layers of plywood and left approx 4" of glass protruding from the laminates, like a tab. When I installed the new transom I wetted out the protruding tab and filled the gap with peanut butter consistancy thickened epoxy. This glassed the tab into the slot. The wood portion of the transom fit within 1/2" of the hull so that was the gap that needed to be filled.<br /><br />I am sorry I have not built the photo gallery yet, but I am getting close.<br /><br />The information I have read seems to contradict what is being said here. I will let everyone know if this type of repair fails in any way.<br /><br />At this stage of the game (and I am not a structural engineer), I don't believe there is a structural problem.<br /><br />Peace.<br /><br />Ed.

 

[Bondo]

Re: Replacing transom from outside

I'm with Jason,..........<br /><br />I'd Never cut up the Original Casting,........Especially at the Transom like that,........<br /><br />I'm Sure it could work with Epoxy,... Not Polyester........<br /><br />It's just the Basic Design Principals,+ My Common Sense that says No Way,......... <br />Do it the Right Way,.. From the Inside............

 

[epresutti]

Re: Replacing transom from outside

Janson,<br /><br />Although I agree with Bondo, if you can, do it from the inside. You can assure the structural integirity from the outside as well.<br /><br />Bondo, I am not trying to create a big debate, I also wanted to double check my work. I am not sure if "Do it the Right Way,... From the Inside" is entirely accurate.<br /><br />I would say more along the lines of the "prefered way". Here is a link to an article that discusses the structural issues and how to make sure your repair is safe.<br /><br /> http://www.us-boating.net/do-it-yourself-fiberglass-repairs.aspx <br /><br />In my case I had a 3/8" thickness of the hull wich by the calculation calls for 4 1/2" overlap on the outside repair, which I have on my repair (actually closer to 5").<br /><br />After reading here I just wanted to double check, it is a little scary to think I am putting a brand new motor on a faulty repair.<br /><br />Based on the extra reinforcement (additional layers of glass, with a larger overlap) I installed, I am sure my repair will be fine.<br /><br />Peace.<br /><br />Ed.

 

[Bondo]

Re: Replacing transom from outside

I'm Sorry Ed,.... I should have worded that differently,.......<br />I'm not dissing Your Work,........ I have all the faith in the world that Your Way will be Just Fine.............<br /><br /><br />I'm just Agreeing with JasonJ,.........<br />

It's just the Basic Design Principals,+ My Common Sense that says No Way,......... <br />Do it the Right Way,.. From the Inside............<br />

That's Just My Opinion..............

 

[eboylan3]

Re: Replacing transom from outside

Ed, the 1996 Gougeon/West System "Fiberglass Boat Repair & Maintenance" guide describes transom core replacement almost exactly as you have done on your boat. Including the 12 to 1 grind out ratio. The only difference I see is that they recommend cutting "...through the skin at the outer edge of the transom, at or just outside the perimeter of the core." They do note that "If you have access, removing the inner skin can mean less work, because of the greater difficulty of finishing the outer skin." So we can see that Gougeon/West System believes that either method is acceptable. Clearly, you don't have anything to worry about.

 

[epresutti]

Re: Replacing transom from outside

Bondo, et. al.<br /><br />One of the reasons I really like this forum is the feedback and constructive comments I seem to always get. If I am wrong, I also like to be set right, my feelings won't ever be hurt when the greater good is being served.<br /><br />Thanks much, keep up the good work.<br /><br />Peace.<br /><br />Ed.

 

[JasonJ]

Re: Replacing transom from outside

Ed, I don't think anyone is saying you are wrong. Just because I don't agree with a method doesn't mean that method is wrong. I am just unwilling to do or recommend this particular method. If a person can do it and it works out, I am all for it. I am just saying that most people who come to this site for help are novices and may not have the skill to do such a radical repair. Doing it from the inside guarantees a much higher likelyhood of success and durability for a do-it-yourselfer. If a person is working with structural boat repair for the first time, a from-the-outside transom repair is way too advanced, and a mistake with that repair can get someone hurt or killed. That is the main reason I am making my recomendations. If a person is a pro and has done it several times with success, then they can do it. Never go off of the "I saw someone/heard that someone do it" deal, unless you yourself has done it or has a buddy that is very experienced to help. I just don't recommend it. Safety first...

 

[epresutti]

Re: Replacing transom from outside

JasonJ,<br /><br />Point well taken, hadn't even thought about the implications for the novice. I was fortunate enough to be surrounded by folks with many years of experience.<br /><br />The block I live on has three registered captains, and boats behind each house on the gulf. Sometimes the problem is you ask three people and get four opinions The guy around the corner works for a boat builder. And I have a very good friend who is a mechanical engineer and another that ownes an aquatic harvesting business with his father, they do all their own modifications and re-builds for their boats. I guess I just took all of that for granted.<br /><br />This was my first rebuild, started in 2000, just getting to the fitting out stage. I didn't do any work without first getting lots of feedback. Read lots of material, posted a lot on this forum and consulted with friends and neighbors.<br /><br />I understand the safety issue and very much appreciate your attitude towards it.<br /><br />Peace.<br /><br />Ed.

 

[jy118lfd]

Re: Replacing transom from outside

Its funny that everyone says to cut the inside.On my aquasport19-6 (73) I was doing the transom and removed the cap to access<br />the wood and I found that the inner skin is 1/2" thick poly and the outer skin is 1/4" there is no splashwell on this boat but the inner skin is definitly the structual component I will try to post pics asap

 

[Bondo]

Re: Replacing transom from outside

I found that the inner skin is 1/2" thick poly and the outer skin is 1/4" there is no splashwell on this boat but the inner skin is definitly the structual component I will try to post pics asap

You Do have an unusual boat there,........<br /><br />I'd Love to see a shot or 2 of it......<br /><br />How big is the Wood, or space Between the 1/4" outer,+ the 1/2" Inner side,.??...

 

[JasonJ]

Re: Replacing transom from outside

That is pretty thick. I have usually seen that the inner skin is so thin that it is clearly there just to hold the transom wood in place. A transom as you describe is a perfect candidate for Seacast....

 

[jy118lfd]

Re: Replacing transom from outside

I will post photos asap It has double 5/8ths ply with poly and mat in between the ply to bond the pieces together. <br /><br />This is the original 19-6 modified v design by Who I think is the founder of aquasport Last name is Sargent

 

[jy118lfd]

Re: Replacing transom from outside

http://www.shareaproject.com/pages/imageDetail,p,168,i,,00.html

 

[jy118lfd]

Re: Replacing transom from outside

I will post more photos and some of the transom with fiberglass cap cut off

 

[BillP]

Re: Replacing transom from outside

I've been around a few pro glass shops and they generally replace transoms from the back. It takes less labor (on innerliner boats) and the work is easier to conceal..but they also have all the adjustable jigs and molds to keep the boat true. They cut on the corners and don't leave tabs to work with either. All structural glassing is done from the interior. When finished there is no sign of work being done. The motor mechanically clamps everything together when mounted so "inside or outside glass thickness" only depends on mass of total thickness and how well glassed to the hull (which is best done from the interior anyway). <br /><br />Also, it is rare for boat mfgs to have thicker exterior glass on the transom than interior. Most use the same layup schedule on the exterior of the transom as the hull sides. Structure is done with the inside glass and ply. None (with far and few exceptions)of them glass between ply layers or do anything special for clamping together either. It doesn't matter whether a low $ Bilgeliner or high $ Pursuit...they do it the same way. If water stays out they last forever.