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Give me suggestions on how to reinforce the transom of a 1961 SPORT 13 boat.

Q1: is there any merit to connecting the transom to the bulkhead [of the engine splash well] via a custom aluminum bracket to provide extra stiffness?

BACKSTORY
On July 2, 2022 I started work [on reinforcement of the transom of a 1961 SPORT 13 boat].


After temporarily installing an engine to get the mounting correct before starting glass work, I noticed that cracks at the corner of the transom at the top, and both sides opened up when I rocked the engine to simulate wave action.

There was fairing compound a previous owner applied perhaps to fix the cracking.

I will make a proper repair to both corners.

I a pleased that the wood inside the transom is solid and that the foam appears dry at least in the areas I had access to, that is, inside the holes I drilled to mount the engine and where I removed the drain tube.

SteveC123 wrote:Give me suggestions on how to reinforce the transom of a 1961 SPORT 13 boat.

From Figure 1 I infer that your 1961 SPORT 13 boat still has its original notched transom for use with outboard engines with 15-inch-shaft and that someone has installed an intermediate plate or mechanism in order to mount an outboard engine with a 20-inch-shaft at an elevated mounting height above the transom.

The best approach for increasing the strength of the transom will be to remove the engine and the intermediate mounting device, and fabricate a new transom with an increase in height of five-inches higher than the original transom. This will require significant work with fiberglass cloths, plywood, and resins.

Without knowing anything about your skill level as a boatwright and working with fiberglass reinforced plastic construction with embedded plywood stiffeners, I can't tell if this modification could be performed by you.

There are some after-market devices specifically designed for fixing the 15-inch-transom height on old 13-footer which can be bolted on.

If there are obvious structural cracks in the joint between the transom and the hull, those defects must also be properly repaired.

For advice on make structural repairs to a Boston Whaler UNIBOND hull, see this article in the REFERENCE section:

Boston Whaler Factory Instructions: How to Make Hull Repairs
https://continuouswave.com/whaler/refer ... tions.html

SteveC123 wrote:Q1: is there any merit to connecting the transom to the bulkhead [of the engine splash well] via a custom aluminum bracket to provide extra stiffness?

Fastening the transom to the bulkhead of the engine splash well would likely add stiffness to the transom, but I don't think it would eliminate the need for proper structural repair of obvious cracks in the transom.

ASIDE: the 1961 SPORT 13 boat was molded 61-years ago. That there are some significant problems in the hull should not be a surprise. There is no basis to assume that the hull became stronger with age. In that light, mounting larger and heavier engines than intended for the original hull is probably not a good idea.

Thank you for the detailed response.

Just to clarify, the engine is a short shaft (15 inch) and the mechanism is a tilt/trim unit mounted such that the engine sits a little higher to go with the setback. The cavitation plate at this point is 2 inches above the keel and the setback is 5 inches.

At a minimum I will do a proper epoxy repair on the corners where the transom meets the hull sides and then look at creating a bracket that ties the upper mounting bolts for the trim unit to the bulkhead. I seem to recall seeing a recent post where a similar vintage boat had rods connecting the transom to the bulkhead, but I cannot locate it now.

Thanks again.

Thanks for the clarification that the engine shown in Figure 1 is a 15-inch-shaft engine.

If the transom engine mounting holes are drilled according to the BIA hole layout for outboard boat transoms, the mounting height of the engine can be raised by three-holes or four-holes (depending on the layout of the engine's mounting plate) without the use of any intermediate plates or mechanism.

I would eliminate the intermediate plate or mechanism see in Figure 1 in order to reduce the weight on the transom. Keeping weight of the transom of a very short boat like a SPORT 13 will improve the boat trim.

For information about engine mounting see these articles:

From the FAQ:

Q8: How Does the Engine Mount to the Transom?
https://continuouswave.com/whaler/reference/FAQ/#Q8

and

Q9: What is the Standard Transom Hole Layout?
https://continuouswave.com/whaler/reference/FAQ/#Q9

From the PERFORMANCE forum:

Engine Mounting Height Nomenclature
An Explanation of the use of the "holes-up" description of engine mounting height to eliminate ambiguity
https://continuouswave.com/forum/viewto ... ?f=7&t=739

and

Considerations in Engine Mounting Height
https://continuouswave.com/forum/viewto ... f=7&t=6618

My 1966 13-foot Boston Whaler Sport had two rods which connected the transom and splash well bulkhead. They were made from stainless steel all-thread covered with a plastic sleeve. A previous owner installed them believing it was a good idea. I thought so too; the only downside was the added clutter in the splashwell.

Thank you Tom. I think it may have been your boat I saw a photo of showing the rods.
I think I saw that you had upgraded to a 16; I hope you are getting some good use from it this summer.

It took some time: the transom corners have been ground out and repaired with epoxy and cloth, and the transom reinforcement is coming together nicely.

This was my first try at welding aluminum—and it shows—but the joints are plenty strong.

The work on the transom reinforcement of the1961 SPORT 13 looks very nicely done.

Q2: are the two connecting rods made from solid aluminum rod or from tube?

Q3: is the fit of the two plates a perfect fit, and, if so, did you weld the rods to the plates while they were in position on the transom and splash well bulkhead?

Thanks for your comments.

The rods are 3/4 inch aluminum tube having 1/8 inch wall thickness.

I fitted the tubes to the plates in situ (a lot of filing) but chose to weld away from the boat to avoid over-heating the fiberglass. This may not have been necessary...

As to the fit, the tubes were butted to the plates within 1/32 inch - any gap was quickly eliminated by the weld puddle.

Very nice job on the fabrication and I am sure that will absorb some of the stresses on the transom caused by the extra leverage of the 5 inch set back of the jackplate. I assume you are next going to through bolt the other side of the plate similar to what you did for the transom side?