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Author Topic:   Why is the transom edge exposed?
John O posted 02-26-2003 09:11 PM ET (US)   Profile for John O  
Why is the top edge of my transom not gel coated? I know that all 17' hulls are this way and they do delaminate (SP). My looks good NOW but should I gel coat it?
jimh posted 02-26-2003 09:30 PM ET (US)     Profile for jimh  Send Email to jimh     

I have been thinking about posting this same question, but more from a point of view of "How do they do that?"

The fact that the two molded pieces (hull and liner) are still in their molds when the they are combined together makes it rather mysterious how the hold this beautiful, precise edge line between them at the transom.

I would love to hear how they get that result.

I think it is truly a detail that is part of the classic Boston Whaler boat "look."

gansett posted 02-26-2003 09:39 PM ET (US)     Profile for gansett  Send Email to gansett     
I don't know why it was done, maybe it was just to show the robust construction. But on the issue of delamination, I don't believe that the "exposed" edge is a problem in itself. I've examined (and owned!) a number of old 16's that have come apart at this seam and it was clear that the solid wood blocks in the transom had been exposed to water that had penetrated the hull. The blocks expand and push apart this seam. The wood can expand so much that the outline of the blocks (as well as the bigger transom block) can be clearly discerned on the surface of the glass.

My theory, keep the transom dry and the seam will not fail.

John O posted 02-26-2003 09:57 PM ET (US)     Profile for John O    
Interesting feeback. I consider my self a new comer to both boats and Whalers as I have now owned my first boat since 5/18/02. I am also pleased that my first purchase was a Whaler.

Along with the ownership and this great site has come a lot of concern about water intrusion. Once again I am relieved to get good information.

John O

Montauk posted 02-26-2003 10:08 PM ET (US)     Profile for Montauk  Send Email to Montauk     
I was told at the factory tour they do that to show and prove the integrity of the hull deck bond. It is done by grinding.
jameso posted 02-27-2003 10:02 AM ET (US)     Profile for jameso  Send Email to jameso     
John O,
This is called the 'Green Line' by BW. It is the interface where the two hull halves are bonded together. I don't think BW thought there would be a problem by not gel coating the area. The exposed edges are simply ground down fair and left. Any delams there can be serious. I have talked to several dealers and the older experienced ones will tell you that it is very important to apply a sealer there.
I have fixed several 15s as well as several of the 17 hulls that were delamimated and it will allow water to ingress to the wood transom..

As Professor Peter Stein (U Arizona) once told me "If you don't test it, nature will".

Bigshot posted 02-27-2003 10:07 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Here we go again....delamination at the green line is VERY common and not an issue as long as the spread area is filled to keep water out. Don't start spreading rumors that if the green line is not tight...yada yada.
John O posted 02-27-2003 08:16 PM ET (US)     Profile for John O    
What can be used to seal this area?
dscew posted 02-27-2003 08:46 PM ET (US)     Profile for dscew    
Boat life caulk can be used. It stays flexible and provides a waterproof seal.
newt posted 02-27-2003 09:58 PM ET (US)     Profile for newt  Send Email to newt     
Cool! Up until now, I thought the previous owners had dragged a lot of crap over the transom. Now I know I am normal. Well, at least the Montauk is.
doobee posted 02-28-2003 01:27 AM ET (US)     Profile for doobee  Send Email to doobee     
When the deck and hull molds are separated there is flat horizontal flange, or moustache, all around the boat. The flange is cut off then ground down smooth. Whaler refers to the green line along the transom as the "transom weld". The reason they leave it exposed is to show off the unibond construction and the fact that there are no mechanical fasteners holding the hull and deck together, as there would be on a single skin boat. If the line does not come out neat, they will touch it up with gelcoat to make it look straight. Sometimes the weld will come out more white than green and they touch it up to make it more green.

When the weld splits open, it is known as a "transom weld failure". Whaler has a very specific set of instructions on how to repair a transom weld failure, and they do not include caulking. They recommend putting a slight bevel on the weld, filling the openings with resin and choped fiber, and then building up the radius with layers of fiberglass.

I suppose similar results could be achieved using epoxy, an adhesive filler, and glass. In either case don't mix the resin too hot, or you could melt the foam underneath.

"I've got an old fat boat, slow but handsom.
Hard in the chine and soft in the transom.
I love her and she must love me,
but I think it's only for my money!"
. . . Gordon Bok

whale on!

Montauk posted 02-28-2003 04:56 AM ET (US)     Profile for Montauk  Send Email to Montauk     
Excellent post Doobee! Thank you.
John O posted 02-28-2003 08:44 AM ET (US)     Profile for John O    
Very nice Doobee
Bigshot posted 02-28-2003 10:03 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Who has a nice doobee?
flyguy posted 02-28-2003 10:26 AM ET (US)     Profile for flyguy  Send Email to flyguy     
good one.
jimh posted 03-01-2003 11:41 AM ET (US)     Profile for jimh  Send Email to jimh     
To doobee,

Please indulge me with some more questions.

I can visualize that the hull part of the joint could extend upward and beyond the joint line, and that it could be trimmed after the molding is complete so that it is flush with the liner. This would result in the exposed laminate we are all familiar with.

But how is the liner trimmed to be flush with the hull?

This must be done prior to inverting the liner and bonding it to the hull, right?

I cannot visualize how the joint can be made and then both elements trimmed afterward. It seems like the liner must be trimmed before combining.


Tom W Clark posted 03-01-2003 03:26 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

They are not both trimmed afterward. Only one skin is trimmed.

I am looking at some cross sections of a 1970 Sport 13 (CSW) that I have sitting on my desk at the moment. At the gunwale it appears that the outer skin (hull) turns 90 degrees at the top of the gunwale and runs about an inch under the skin of the liner which runs the full width of the gunwale cap.

The transom cross cut is more interesting. It appears to my eye as if the cloth of the liner runs the full width of the thickness of the transom and doubles back under and folded back and forth several times in a sort of bunched up series of S's that (with the addition of resin) make up a solid 3/4" of fiberglass on top of the plywood in there.

The outer skin (hull) seems to go straight up and be trimmed flush with the top of the transom. forming its bond along the c. 3/4" vertical thickness of the bunched up glass and cloth of the liner.

So, to summarize, it seems the liner caps the hull skin everywhere except the transom where the reverse is true. Thus the green line is exposed to the side on the gunwale and on the top at the transom.

doobee posted 03-01-2003 10:28 PM ET (US)     Profile for doobee  Send Email to doobee     
The mold that is used to build these hulls is not like your traditional single skin mold. You could say it is the Boston Whaler of boat molds. The male deck mold is placed over the female deck mold in such a way that the overlapping hull and deck laminates are sandwiched between the molds and the pressure of the foam. The molds are joined at, or just below the top edge of the gun'l. The overspray on the hull mold is folded back over the hull to form the 90 degree turn at the gun'l which Tom described.

Ever since I read the thread about CSW I have been trying to remember the purpose of the yellow poly rope that Tom found embedded in the hull. Could it be that the rope was there to keep the hull laminate from doubling back on itself prior to foaming?

The overspray on the deck gets sandwiched between the hull and deck molds when they are bolted together. This is the moustache that gets trimmed off after the molds are pried apart.

I hope this helps some it's hard to describe without a diagram and my memory just aint that sharp. Too much FG fumes I suppose.

whale on!

Tom W Clark posted 03-02-2003 02:34 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
The yellow polypropylene rope was there for the purpose of venting the air from the molds as the foam expanded. The polypropylene rope is no longer used. The aluminum conduit may still be used for this purpose.
frank_king posted 03-04-2003 07:06 PM ET (US)     Profile for frank_king  Send Email to frank_king     

have you ever had to seal up the transom edge of a whaler?

jimh posted 03-05-2003 08:18 AM ET (US)     Profile for jimh  Send Email to jimh     
This image shows what we are talking about:

I would really like a good sketch of how the molds and layup are done. Can anyone send me one?

Tom W Clark posted 03-05-2003 10:31 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

No, I have never repaired a weld failure. I have seen a few though. Just a couple weeks ago I was inspecting a 1981 Montauk that had lived a hard life in Alaska. This was a hull built to commercial specs as witnessed by it's red dot of gel coat on the sides.

Almost the entire transom weld had opened up and apparently been open for some time as somebody had tried to apply some gel coat patch paste and caulk in there to seal it up. The gap had widened even beyond where it was at the time of those repairs.

Presumably the weld had failed because the plywood in the transom has gotten wet and expanded. There was absolutely no movement of the fiberglass skins. The transom was rock solid, but the gap was as much as 1/4 in places.

doobee mentions Whaler having specific repair instructions for this type of failure. Does anybody have these instructions documented on paper? It might make a nice addition to the reference section.

My Friend John had an 1988 Outrage 18 that he bought in 1991. It had a minor weld failure to one side of his motor. It bothered him enough that he had it professionally repaired by a fiberglass shop. Somehow he got his insurance to pay for the repair and when he got it back you could not tell there was ever a problem.

Knowing what I now know, I would want to repair any transom weld failure ASAP and I would want to do it right and be done with it.


Can you be more specific about what sort of a diagram you want? Send me your FAX number and Ill see what I can do.

kshoaps posted 04-23-2003 04:28 PM ET (US)     Profile for kshoaps  Send Email to kshoaps     
It seems odd that BW would purposely leave a potential weak spot just to demonstrate how well built the boats are.

Sorta like drilling a hole in the hood of your Cadillac to show that the metal is galvanized.

doobee posted 04-23-2003 09:35 PM ET (US)     Profile for doobee  Send Email to doobee     
It is not a potential weak spot. It runs all the way around the boat and never fails, except at the transom. The transom is the only part of the weld that includes a large piece of wood as a structural component, and with the engine pushing on it, the wood can act like a giant wedge, or pry bar, forcing the weld open.

This problem is not limited to Whalers. I doubt that you could walk into any boatyard and not find several examples of structural failure where the fiberglass and the transom reinforcement come together. In fact, I would guess that you'll see more non-whalers with this problem.

Nobody is perfect. It is the combination of hull design, performance, and the ability to park a bulldozer on top that makes the Whaler such a great boat.

jimh posted 04-23-2003 09:55 PM ET (US)     Profile for jimh  Send Email to jimh     
At most of the gunwale on a Whaler where the hull molding meets the deck liner molding a slight overlapping flange may be tolerable, but it would seem that at the transom, in the area where the engine is going to mount, the joint would have to be flush so as to provide a nice flat top to the transom.
lhg posted 04-23-2003 09:58 PM ET (US)     Profile for lhg    
My 18 Outrage does not have this green line like my old 16 had. It is completely gelcoated in the desert tan color. Nor are there any signs of delamination there. I have never seen delamination on a second generation Outrage transom. Was something done differently?

Now I notice on the new boats, even the Guardians, that a cheap looking plastic angle is used to cover this previoulsy well finished seam. Simply cost cutting? I don't like the detail.

John O posted 04-23-2003 10:19 PM ET (US)     Profile for John O    
I'm with JimH on this. Why not gel coat this area at the factory? The other areas are covered by the rub rail. I am of the opinion that the addition gel coat could not hurt and would give my that warm and fuzzy feeling inside.
doobee posted 04-23-2003 10:55 PM ET (US)     Profile for doobee  Send Email to doobee     
Gelcoat serves no purpose as a sealer or structural component in this case. The weld will fail regardless of gelcoat.
John O posted 04-23-2003 11:10 PM ET (US)     Profile for John O    
What about Gel coat as a moisture barrier?
doobee posted 04-24-2003 01:43 AM ET (US)     Profile for doobee  Send Email to doobee     
Gelcoat is not a moisture barrier. It's primary function is to provide a nice looking finish, and to make it easy to pop the hull out of the mold.
SSILVER posted 04-24-2003 10:22 PM ET (US)     Profile for SSILVER  Send Email to SSILVER     
I had a small amount of delam on my 1981 Newport, just cleaned it out w/ a dremel tool and used a little West and clamp to rebond it. Then I scuffed the exsisting dull green line taped it off and put a light coat of West on it.
doobee posted 04-24-2003 10:42 PM ET (US)     Profile for doobee  Send Email to doobee     
West or other epoxies will do a good job of sealing a weld failure, however, epoxy will degrade when exposed to sunlight. Once you have applied the epoxy, you have to cover it with something to block the U/V rays (gelcoat, paint, or varnish).
PMUCCIOLO posted 04-25-2003 12:56 AM ET (US)     Profile for PMUCCIOLO    
Both of the CPD hulls I've bought have a black molded trim which covers the transom edge perfectly. The covers are secured by black silicone and screws.


SSILVER posted 04-27-2003 11:47 PM ET (US)     Profile for SSILVER  Send Email to SSILVER     
I am thinking about doobie response. Will West weather that quickly? The original exposed weld held up pretty good for over 20 years. Would seem that a couple layers of West would buy quite a few years. Unless I hear diffrent I think I will leave it exposed, looks like new now.

doobee posted 04-27-2003 11:59 PM ET (US)     Profile for doobee  Send Email to doobee     
The resin used in Whalers is not epoxy and is not subject to the same degredation. I used some West System on a repair on my house. It did not get painted before winter, and by the following spring it was peeling off. People who make custom surfboards take steps to protect the epoxy from U/V. You can use West 207 special coating hardener, which has U/V inhibitors in it.
SSILVER posted 04-28-2003 12:08 AM ET (US)     Profile for SSILVER  Send Email to SSILVER     
Thanks doobie, I will put that on my shopping list! Sounds better then gelcoat or varnish.

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