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Author Topic:   How to build up notched transom - 1965 13ft
Rob P posted 05-23-2002 05:03 PM ET (US)   Profile for Rob P   Send Email to Rob P  
Having researched this forum and lots of catalogues for jackplates/extensions, I have decided I need to build up the transom notch with wood core and fiberglass. Since it was originally designed for a 15" shaft outboard and I want to retrofit it for a 20" shafted motor, do I need to raise it exactly the 5 inches to get a proper placement of the new prop? This will put the remodelled addition above the old transom line. "Notch" will become a "Raised 1" bump". Do you agree I should raise it 5"? or does anyone have a better solution?
JBCornwell posted 05-23-2002 06:18 PM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Hi, Rob.

I wouldn't try to produce a full-strength 20" transom on a blue-liner 13 by putting a block on top. I know it has been done, but I would not buy one that had been so-modified.

I think an extender or jackplate is a safer alternative.

Good luck.

Red sky at night. . .
JB :)

Highwater posted 05-23-2002 10:13 PM ET (US)     Profile for Highwater    

What is the distance (measured along the hull) from the top of your notch to the bottom of your hull? I know it is more than 15".

Could anyone who owns a post-1972 13' give us this distance on their boat? We might find that there is only a four inch difference.

vdbgroup posted 05-24-2002 12:06 AM ET (US)     Profile for vdbgroup  Send Email to vdbgroup     
We raised transom to 20" on our 1970 13' restore project. Outstanding work by a talented glass man. Solid as a rock. If you raise it, do it right.
13sport posted 05-24-2002 12:06 AM ET (US)     Profile for 13sport    
There are still quality engines being offerd with a 15" shaft. It does not make any sense at all to build up your transom to accomodate a 20" shaft. Check out tohatso outboards ( I know mis-spelled it) A new engine will last 10-15 years. How long will a back yard transom patch last?
Highwater posted 05-24-2002 08:22 AM ET (US)     Profile for Highwater    
The 15" measurement is a vertical distance, going from the top of the transom straight down to where the horizontal plane of the bottom of the boat intersects that line. Since the transom does not go straight down, the actual height of the transom on pre-1973 13' Whalers is--I believe--17".

Could someone with a post-1972 13' please measure the actual distance from the top of the transom to the bottom of the boat? Thanks!

JFM posted 05-24-2002 10:02 AM ET (US)     Profile for JFM  Send Email to JFM     
Rob, I have had 3 13Sports with 15" transoms. There are various ways too address this issue.

You can build the transom up with wood and glass.

You can build the transom up with wood only (I have done this using teak) however, you have to cut the wood to fit the bend in the transom.

You can use a 15" motor.

You can use a 20" motor with a jack plate.See

My last venture I used a 15" motor with a CMC adjustable jackplate. I used the jackplate because the new motors are not bolt on anymore, you have to drill through the transom and the bottom bolts are under the water line and are blind on the inside. I would have used a 20" motor and fixed jackplate if I had to do it over again, but I got a steal on the 15" motor. Regards, Jay

Tom W Clark posted 05-24-2002 12:49 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

As JFM points out, you have all sorts of options. All of them work. They all have advantages and disadvantages. There are photos of most of these mounting in Cetacea and many, many threads discussing the different options.

You are correct when you note the distance along the transom of your boat is greater than 15". The 13" Whaler has a very pronounced slope or "lean" to it. The angle on the Desert Tan 20" models is the same and thus the distance along the transom will be greater than 20" but again the vertical distance as measured perpendicular to the keel will be about 20".

Transom heights, as well as shaft lengths are not exact nor do they need to be. With the many different mountings and adjustable bolt holes on the motor brackets there is necessarily room for adjustment.

The transom on the 20" models is almost exactly like a notched transom model but with the line of the top of the transom continued across without the notch. It does not go flat where the notch would otherwise be but continues in a curve. Explore Cetacea for many views of this.

There's nothing terribly wrong with using a 15" motor. Tohatsu seems to be the one manufacturer who makes a 15" two stroke with power trim and tilt. Depending on what you really want, your' favorite motor may not come in a 15" shaft.

Bill Aucoin converted his 15" shaft to a 20" by making his own stainless steel bracket that filled in the notch. I was impressed by the design which does not allow water to slop into the boat as a bracket or jack plate will. Here is a photo of Bill's boat:

Highwater posted 05-24-2002 04:41 PM ET (US)     Profile for Highwater    
Clark--would you ask Bill if he has any interest in selling copies of his stainless steel insert? Or would you mind telling me how I might get in touch with him? Thanks! David
Highwater posted 05-24-2002 09:45 PM ET (US)     Profile for Highwater    
I meant to address my last post to "Tom" not "Clark." Sorry, Tom Clark. I greatly appreciate your comments.

There is one other option that you have not mentioned, Tom. That is, mount the 20" shaft motor on the 15" transom and leave nothing but air where the notch is located. The motor does not rest on the top of the transom but instead it is supported entirely by the four through-transom bolts. I know that this sounds like a crazy idea but that is how my 1987 40 hp Johnson is mounted on my 1972 13'. I bought the boat that way, and I believe it has been that way since 1987. The previous owner and I have done a lot of water skiing with this boat, and have not had any problems. When I get the money to repower, I plan on putting in the CMC vertical extensions (or your friend's stainless steel insert) and teleflex steering. But for now, it seems to work fine as it is. The cavitation plate on the engine is just below the hull. It has a top speed of 34 mph with 12 gallons of fuel and just me (190 lbs) on board. It will get on a plane carrying 800 pounds. The transom has no stress cracks.

Tom W Clark posted 05-25-2002 01:05 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

I will send an email to Bill Aucoin with your email address as well as ask him to respond in this thread with more particulars about his bracket.

Bill had contacted me with questions about the restoration of his 13'. When he got his boat back form being painted he sent me some photos of it including the above shot of the bracket.

I really think it's a nice piece of work. I asked him about the expense involved thinking it might be something others might be interested in too. Apparently it was fabricated be a friend or neighbor or something. Let's hope Bill responds with more information here.

Scratchin Bill posted 05-25-2002 09:32 AM ET (US)     Profile for Scratchin Bill  Send Email to Scratchin Bill     
As Tom mentioned, a neighbor fabricated the transom plate out of stainless for me. I didn't weigh it prior to installing but I would guess around 10 lbs. I through bolted using 6 ss carriage bolts and plenty of sealant around the edge and bolts. I then applied a bead of seatlant around the whole plate once it was bolted on.
John made the plate from 3 pieces of stainless. The back, front & top. he also measured my motor and welded 2 gussets under the engine clamps between the front & back plates to ensure the plate would not flex or crush. It fit just about perfectly other than I had to grind down 1 high spot in the glass & gelcoat.
Since the picture Tom has posted I added two turnbuckles from the engine clamps to the bottom, outside, throughbolts. I also made some wedges out of mohogany to try to provide a flat surface for the motor to mount to on the back. I have been testing the motor height and once I am comfortable with the position I will through bolt the motor permanently.
I highly recomend the turnbuckles or some sort of safty devise if you plan to have your motor metal to metal. I also places some 1/4 inch rubber patches under the engine clamps.
My e-mail is if you would like a more recent front & back view.
I will also speak to my neighbor and inquire to him making more of these if anyone is interested. I installed the plate in under 1 hour and could be removed to restore the original status of the boat if desired.
Scratchin Bill posted 05-25-2002 09:40 AM ET (US)     Profile for Scratchin Bill  Send Email to Scratchin Bill     
The stratchin part of the handle was from the sanding portion of my project and not any kind of social or hygene problem.
I hope I never have to sand fiberglass again!
DaveNJ posted 09-23-2002 02:11 PM ET (US)     Profile for DaveNJ  Send Email to DaveNJ     
I know I am digging up an old post but I was interested in others input or experiences.

I am also thinking about raising the transom on my 1968, 13' whaler to accept a 20" shaft motor I just bought from another forum member. I would rather not just stick on the mini-jacker or CMC extensions. Now I am not sure of the integrity of the old wood inside the transom.

I spoke with Wolfgang Unger of
[[/url] and he said he has done several Whalers with the Sea Cast material.

Briefly, he told me these steps to raise the transom: Remove at least 4" of inside material around notch, make mold to conform to transom curve, grind edges (angled scarf) of remaining transom inner and outer "skins" to accept fiberglass skins that will fill old notch area. Layup fiberglass on waxed mold, Put at least a layer of 1 1/2 oz matte and 24oz woven roving for the inner fiberglass. For the mold, the easiest way is to use 1/4" tempered masonite - this will make the curves you need.
Make sure to leave about 1/4" extra and feather it in to the existing fiberglass, pour in SeaCast material, finish top, Let cure, apply gelcoat.

I know it is a lot of work, but I was wondering if anyone had done this.
Mr. Unger did say he always has encountered rotted wood inside of transoms he has repaired, even the whalers.

Any thoughts ?

whaler131 posted 09-28-2002 08:45 PM ET (US)     Profile for whaler131  Send Email to whaler131     
I have a 11 tender and put a jack plate on the back, bolted through the top and then on the bottom used lag bolts this lets me use longer shafts and lets me get into skinny water on the flats. This way i did not have to mess with the boat It adjusts for 20" or 15", i can set it for even shallower water if need be. good luck
David Jenkins posted 09-28-2002 10:39 PM ET (US)     Profile for David Jenkins  Send Email to David Jenkins     
Why do you suspect that the old wood inside the transom has rotted or cracked? If it is, how would filling in the notch solve that problem (you'd be building on a weak foundation).

I'd go with the jackplate or CMC vertical extensions. But if you wanted to be extra, extra safe, why not fill in the notch and use the CMC vertical extensions?

DaveNJ posted 09-29-2002 04:07 PM ET (US)     Profile for DaveNJ  Send Email to DaveNJ     
That is what I probably will do. I bought the mini-jacker but I don't like that it has to overhang the top transom by 2" in order to get the right motor height. Not enough mounting holes left for me to feel comfortable with that. I am sending back. I will try the CMC extensions and fill in the curved notch with a bent mahogany plywood laminated with epoxy. Another option: I am also waiting to here back from Bill Aucoin to see if his neighbor can make me a stainless transom plate, like he has.

Wagon1 posted 09-30-2002 08:48 PM ET (US)     Profile for Wagon1  Send Email to Wagon1     
This topic comes up all the time. I have a 72 I restored 2 years ago. I put a 02 15" Merc on her, and it screams. If you want to put a 20" shaft on a 13, buy a 73+. In my opinion, a "jack plate" on on old 13 looks silly.

Just my .02


DaveNJ posted 10-01-2002 09:06 AM ET (US)     Profile for DaveNJ  Send Email to DaveNJ     
Mike -

I have a 1968 13' whaler that I bought for $500. I got a great deal on a mint 20" shaft motor from fellow forum member. I don't have a lot to spend so I am trying to do the best with what I have.

Telling me to now get a post 1973 hull and telling me that a 20" looks silly is your opinion and does not really benefit anyone or add any creative solution in this "Repair/Mods" section of the forum.

You are entitled to your opinion of course. I just wish it was a more positive or helpful one to me and others who may be in the same situation.


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