Transom Replacement Planning Help Needed.

Greetings All.

I've been doing a lot of reading here. My boat, a 21' express cabin, 8'1" beam, definitely needs a transom VERY soon. When the 150 outboard was replaced, the mechanic tightened down too much on the bottom bolts, crushing the transom a bit. Since then, it has softened VERY quickly!

Because there is NO access to the inside of this transom, I was considering going the SeaCast route. But I've read here that there are some doubts about the material, and that going the plywood/epoxy method is really the best way to do it.

Do any of you who are experienced with replacing a transom from the outside have any general ideas on the material costs and hours of labor?

Here is how I'm GUESSING this should go. PLEASE feel free to correct or suggest as you see fit!

1. Remove the aluminum transom cap
2. Cut the outer skin @ 4" away from the edges of the transom and remove.
3. Remove all wood from the transom, clean, dry and scarify all fiberglass.
4. Cut plywood sheet 1 to size, following the plane of one side of the V bottom.
5. Cut sheet 2 to size, following the plane of the other side of the V, creatng a 17 degree angle between the grain of the two sheets.
6. Wet the inner wall with epoxy, apply 1/8" matting, wet out completely
7. While still wet, apply inner sheet of plywood, apply thickened epoxy liberally to both sheets, and then apply outer sheet of plywood, and then squeeze everything gently together with a few screws.
8. Immediately after the epoxy has set, remove screws, and fill screw holes with fillet mix
9. Then apply a wet layer of woven roving and re-apply the removed skin using duct tape, formica, plywood and braces to hold in place until set
10. Let cure so as to be able to change over to polyester resin?
11. Fair the cuts areas with regular resin, sand all, and spray fresh gel coat.

The above is what I have distilled from reading. PLEASE correct me where I'm off.

I'm guessing the demo and prep time will be about 2 days, the actual replacement time will be 1 day, the fairing and gelcoat time 2 days. This gives a total of approximately 5 working days, with a fast helper needed during the re-install.

Does this timing sound too fast? Too slow? About right?

Any ideas of the approximate cost for the above (needed) materials?

Or does anyone think I should go the SeaCast route? I'm thinking materials for that stuff will run me $400-$600, with approximately 3 days of labor, for reference.

Thanks!

-TH

 

you should see if you can remove the transom from inside, its harder i know, but you will keep the shape square and cut down on the glass work, i always try to remove from the inside it can be a real pain to do, the thing is a rotten transom is a telatail sign the stringers are bad as well. dont use polyester over epoxy it wont stick, seacast works but iam a traditionalist, i like wood but alot of guys are using seacast, labour time is hard to say u dont know what u got to u see it in a shop they cost anywhere from 3000 to 6000 for ur size of boat and often they just break even lots of labour

 

I also try to do the inside skin if there is one, the budget permits and access is reasonable. The exterior skin remains intact so the boat looks the same. Sea Cast is a polyester core material and has limitations. Of course the inner and outer skins must be up to the task to act as structural skins, bonded over a core. Many boats have a thick hull and a liner or deck cap/liner combo, which is very thin and can't be relied on for sandwich construction, without additional reinforcement. The liner on these boats offer interior accommodations (furniture, bait wells, etc.) but not enough bulk or stiffness to act as an inside skin. I've recently completed a transom, where the plywood was bonded directly to the hull shell, tabbed into the sides and bottom, with no interior skin at all. In these cases, Sea Cast can't be used without additional construction, of a sufficiently stiff inner skin.

Plywood on the other hand, offers considerable reinforcement once bonded to the hull shell. There doesn't have to be an inner skin, nor a liquid tight seal between the inner and outer skin, in which to pour something like Sea Cast. On many boats, particularly cored transom craft, Sea Cast can be a solution, but it isn't the transom in a can, that many think it is and does have limitations in certain applications.

I would add, grind back all the hull shell edges which were cut to remove and gain access to the rotten transom material. These areas get filled with a few layers of cloth, then filler to fair things up. I try to match the hull laminate schedule with the beveled area voids. In other words if the hull is 1/4" thick, I place about a 1/4" of new material in the ground out (beveled) areas with room to fair things up. These tapered back seams are a transition from the old, through the new, back to the old 'glass and should be generously beveled for maximum strength and adhesion.

You'll be surprised how long it takes to get the old transom material out, grind and bevel clean the faying surfaces. I wouldn't want to hazard a guess at your skill level, available tools, work environment, etc. so time allotments and costs will be something you will have a better handle on, once you've jumped in and seen what you're up against (and why it cost so much to have it done professionally). Good luck . . .

 

To thill:

Difinately, wise to heed a fellow who's call sign is: fiberglass jack.
Also PAR, I'd suggest, is making sense.
Here's a third guy in agreement. - And when three people are all singing the
same tune........

First, consider that your mechanic is most likely blameless. Especialy, if your
vessel is well past it's warrentry period. They may have done you a favour.

As the transom, if it's built right should have no trouble resisting any torque
loads that can be generated by hand.

Consider:
At speed, the forces trying to rip your transom right off the boat.
- Take the hp; plus the weight of the O/B - on one side of a tetter totter.
- On the other side is the full weight of the boat; plus the force of each
wave impact pushing the bow up.

These opposing forces all meeting at the fulcrum: - Your transom.
So repairs at this point can not be taken lightly.

Solutions:
I've built boats with epoxy and wood - with no rot after 25 yrs.
That does not mean, a series production boat will have such longevity....
It does, mean, however: that repairs with epoxy and plywood can be
very effective.
If ....good practice is followed. -This sentance needs to be under lined !

Also, make note:
- Both gentlemen, zoomed in on:
- Concerns with the INSIDE of the vessel. Right away.
- As rot, almost always starts: INSIDE the boat. Most likely.......
- The very fact that access sounds limited, is another powerfull reason:
- TO, in fact; gain access to the interior of the vessel.

A few more unavoidable elements:
- Epoxy, is very resistant, to the intrusion of water....AFTER it's cured !
- When it's being applied - bone dry - is the phase to keep in mind.
- While it's cureing, even high humidity, can be a concern.
( There maybe, some esoteric ones that, on the side of the can will say,
" Can be applied under water.." But already; you are spending lots
- on regular epoxy.)
- So, good practice - requires drying the boat out. Especialy the interior.

Finaly: And I'm giving out a trade secret here - I always put more F. Glass
or Carbon Fiber - on the inside - face of the core material.
- Because the inside, is where structural failure usualy starts. Even if; the
impact comes from outside of the boat.
So, as the fibers, are intended to resist tension, or tearing of the material.
It better serves resistance of the total composite - to have more tensile
fibers inside the craft.

Do I need to use the word " inside " a few more times.... or has the
point been made ?!

We are all; trying to be polite, because everybody loves their boat.
But there is no " forever " boat and untill it is opened up it's going to be
difficult to really know what's required.
Or worst of all - how much it's going to cost.
Or how many marriages will dissolve during your long days
- working on the boat.

Good Luck and Fair Winds !

 

Thank you!

Gentlemen,

Thank you very much for the replies and help.

The mechanic used a 3/4" air impact gun. It crunched the outer glass a little, but it was solid at the time. This year, after one day on the water, there is noticable flex under the two bottom bolts where the glass really crunched up. It's soft, now!

I'd like to go from the inside, but in this boat, the liner, the motorwell floor, the gas tank, two bulkheads and a fishbox totally block access to the inside of the transom. I can barely see even 12"x12" of the transom through an access hatch. But it looks like heavy woven on the inside, which may be good.

Fortunately, and strangely, this boat has glass/foam sandwich stringers and floor and bulkheads, (Marine-Core Construction they call it) coupled with a wooden transom, and a totally untreated, plywood storage box, which also needs repair. It's a strange mix, if you ask me.

Anyway, It's late, but I'm going to study each of your responses tomorrow, and try to extract the information from them.

But I'm thinking, IF the inner glass is as thick as it looks, perhaps I should look into the seacast a little more before making any hard decisions. Research ahead of time beats wishing you had later. And honestly, this boat isn't worth putting a ton of money into. It's not that great a boat even when it was new.

Fiberglass Jack, you say "lots of guys" are using the Seacast. Any horror stories? Thanks again.

-TH

 

some times you got to remove all the stuff in your way, gas tank motor and so on thats why it costs so much, ive never used seacast ive read lots about it, the stuff is no more than bondo with recycled filler added, who in there right mind would add floor sweepings to a new product, so right off the bat i dont trust it, its great that they recycle but i would prefere to have new matereal , it works and there website does have a lot of good testamonys from customers, iam just old fashion go to there website and u will see

 

we use a product by the name of COOSA it is a rigid material like plywood but is 45 % lighter and has a .1% water absorbing rating . just resin it on the side towards the inside of the transom and then use plexis to glue it in place ,if you want you can put a layer of mat on it before you start ,once you have it built up to the thickness you want ,you can start adding layers of glass until you outside skin is back to the thickness needed and the just fair it and paint . also coosa saws etc with just normal wood working blades .etc.

just an option
tb

 

Hmmm..... I'm going to have to think about this, now.

Getting to the inside of the transom is practically impossible. I just took a look, and I had FORGOTTEN about the "wall" bulkhead just forward of the gas tank. I'm guessing it is there to stiffen the structure, and it looks vital.

I'm hearing that cutting the outer skin is NOT recommended. Does it really compromise the structural integrity that much??? I'd hope that with this full bulkhead 4' forward of the transom, the shape shouldn't distort too much if I cut the middle of the outer skin off. Any thoughts on this?

I just took a look at the Seacast website, and their testimonials seem pretty impressive. (As does every claim of every company in the world) Bondo is mostly sandable filler, so I'd guess this stuff is a bit stronger. But I'd like to see some of the failure stories too, to get a more balanced picture. I'm going to search the web for some now.

Also, I did a rough estimate, and I'm looking at almost $900 in Seacast material alone. That's over double what I estimate my plywood, resin and glass costs would be.

Ugh.....

-TH

 

Removing Outter Skin

Removing the outter skin isn't that big of a deal as long as when you are getting ready to replace it you grind and sand back gelcoat and make very sure you are going to have a good bond all around ,we build boats of all sizes and do yard repairs and we do alot outside /in repairs for reasons just like yours . if you have prepared all sufaces right and then put the proper amount of layers etc you will be fine .

tb
could you pass the seacast website address along to me please ? i am interested in seeing just what they are selling !

 

trawler builder what out fit are you with

 

fibreglass Jack ,
I own and operate Apple Island Marine Boatbuilding and Repair , have a look at our website www.appleislandmarine.com.
We are located in Nova Scotia .How about yourself ?
TB

 

Update

Gentlemen,

Thank you for the continued information, especially you, Trawler Builder, regarding cutting the outer skin.

After the last series of posts, I decided to look further into the Seacast route. I searched the web, and found nothing negative from anyone who had used the stuff. (Actually, Par, you came up a lot in Google.) Then I talked to several people at Seacast. I was impressed with their patience with all my questions. With permission, I got the phone number of a local marina (Lake Anna) that repairs using Seacast, and a guy who lives close to me, who did his own.

Now THAT is what I really wanted. I called him up, and he told me how happy he was with the stuff. I started to ask more questions, and he asked why I didn't just come on over and see for myself.

And THIS, I think you will find interesting....

His name was Joe, he is a local auto body-shop owner, and he has a 20' boat similar to mine. He was very kind and took the time to explain how he did it, how long it took and so on.

Despite the manufacturer's recommendations to remove all of the transom wood, he didn't want to spend too much on "an experiment", so he only cut out the center section, between the two intersecting walls of the motor well. After vacuuming it out, he filled it with acetone and put a couple of heat lamps on the transom, and left it for several days.

When he got back to it, he cut some notches into the center of the core to give the seacast a "tooth" into the existing structure, and also to check for moisture. The sawdust was dry, so he went ahead and poured.

He said he was worried about the heat it produced, but that wasn't a problem, and nothing warped or discolored. He used a single 5 gallon bucket. After a couple of days, he re-drilled and re-mounted his engine, and he has been perfectly happy ever since. Surprisingly, this was FIVE YEARS AGO! He said he figured if he got a year or two out of it, he would be happy. Now, he says he's keeping this boat as long as it lasts, since it's paid for.

I have to say, I was impressed. The boat looked like nothing had been done. He told me to rock the motor, and then told me not to be scared, so I really rocked it, and that transom really is rock-solid. I would definitely be happy with this transom!

He showed me a pancake blob of it from when he did his, and it seems like tough stuff. I asked him whether it floats, and he says it really does.

Joe is a very cool guy, and due to his mechanical background, we had a great, technical conversation. I almost feel like an expert on this subject, now. That's going way above and beyond in my opinion. And he's offered to help when I'm ready to do mine!

As you can imagine, I'm very impressed, and I'm completely sold. It really is impressive when you see it in person.

After this, my only dilemma is deciding whether or not to do a full or partial replacement. My transom is different than his, and there is no good breaking point, like there is in his. But I'm starting to think for $900, it's worth the peace of mind to do it according to the manufacturer's instructions, especially seeing how simple it appears to be to do.

Sorry for the long post, but I thought it would be useful to others if I posted this. Once I make up my mind and start the process, I'll start a post and take pictures as I go, unless anyone objects.

That's the skinny, so far...

-TH

 

The "experiment" your new friend has preformed on his transom will likely fail. The key to a core materials use is the absolute bond it must have with the inner and outer skins of the sandwich construction. The core material has no real strength as a stiffening material. It works because the inner and outer skins are bonded to a core material that doesn't compress, which keeps the skins separated, thereby providing the strength to the structure.

Just vacuuming out and sloshing some acetone around isn't going to get the inside surfaces of the skins clean enough to provide a good bond. A bad core bond is the world's end to any cored assembly.

Imagine that, lots of wonderful testimonials on a web site promoting their product. That's what I love to see, lots of folks, none that understand the chemistry, physics, dynamics or engineering of the products, materials or application offering their opinion on a subject they, if pressed for an honest answer, clearly don't have a clue about.

Yes, you can cut the outer skin and often times you have no choice, because of the amount of disassembly or difficulty gaining access to the inside. Sea Cast is a core material, not plywood in a can. It will work if the two skins are thick enough to permit their use in sandwich construction, either alone or with additional bulk added, typically to the inner skin.

 

Par, Ive givin up , u can tell them but they dont listen, this seacast is the greatest thing since slice bread. just pour and go, and off u go, i really looking forward to seeing this crap fail, in a few years there is going to be lots of work to be had fixing seacast, and i love the way them guys clean with acetone , all they are doing is shifting the dirt around the dirt wont evaporate with the acetone and dont forget the water that will be traped in the fiberglass can u say ossmossis, man all they are doing is band-aiding the proplem,, when i replace a transom i will gring alot of the old glass away, and if iam going to use polyester resin i will use a transition resin like derakane to insure a best bond posable, they only subsatute for ply is coossa board in my opinion, and going from the outside u are adding a **** load of refinshing work guys are to lazy to do the job right i know its hard to do from the inside but who said boat repair is easy , ive been a week or more tearing plywood out its not always totaly rotten, the cost we pros charge is not that high, and if the job is done right its good for a long time ive never had a transom come back, then again i will not band-aid. all i can say is go around to the boat repair shops and request that they use seacast, they guys working out of the back of there vans probally will do it, but a guy who respects his name in the trade will be a different story

 

Par,
First, let me say, I've been reading the archives here, and I appreciate all of the time and effort you have dedicated to helping others fix their boats. You have certainly earned my respect! (And also Fiberglass Jack.) I notice that you both seem to be careful to only offer solid advice.

So, I definitely value the concerns you mention. In response, I honestly don't know WHAT the inner skin of my transom is like. My boat is off getting serviced, but I will find out soon.

Two things impressed me about the Seacast repair in person. First, was how absolutely solid his transom was. Second was the fact that this is after 5 years of regular use in the Bay. (which means lots of pounding)

I see you helped a member, "johnsonmtz" on this forum three years ago, and he reported good results with Seacast. I wonder how that repair is doing now? Is he still around? It would be nice to know.

Anyway, I'll post what I find in my transom when I get my boat back.

Thank you for the help and the feedback!

-Tony