1969 CURRITUCK 16 Engine Mounting

Optimizing the performance of Boston Whaler boats
Ziptide
Posts: 2
Joined: Sun Jun 16, 2019 1:30 pm

1969 CURRITUCK 16 Engine Mounting

Postby Ziptide » Sun Jun 05, 2022 10:39 pm

I have a 1969 CURRITUCK 16. I just purchased a new Yamaha F70 engine to replace a 2000 Tohatsu 90-HP two-stroke-power-cycle engine. The engine mounting holes on the F70A do not line up with the current holes in the transom. Because of the shallow engine splash well, the old engine was mounted using two lower bolts that threaded into a boss in the engine bracket of the Tohatsu. The F70 engine mounting bracket does not have a threaded boss at that location. Any help [to resolve this problem] will be greatly appreciated.

COROLLARY:
If the only solution to the engine mounting problem is to get a engine jack plate, should I upgrade to an hydraulically operated jack plate?

-Sam

[Moderator's note: this thread has moved to PERFORMANCE for discussion. The PERFORMANCE forum is the best place to discuss problems related to re-powering.]

jimh
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Re: 1969 CURRITUCK 16 Engine Mounting

Postby jimh » Mon Jun 06, 2022 5:57 am

The old engine was mounted using what are called blind mounting holes. This design for the engine mounting bracket was once common, but modern engines no longer have that blind threaded boss as part of their engine mounting bracket layout, as you discovered with the Yamaha F70 engine. (If you just bought that engine I hope you got the newer model F70A engine.)

The problem of mounting an engine using the BIA engine mounting bracket and hole location on older Boston Whaler boats that have shallow engine splash wells is a very common problem. The solution is described in the FREQUENTLY ASKED QUESTIONS.

Please visit the FAQ in the REFERENCE section of the WHALER section of the website. Read the FAQ answers to your question at

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

The FAQ contains very carefully written answers to very common questions. You will find all the information you need to solve the engine mounting problem.

With regard to buying a jack plate, that is a possible solution. My preference would be to not use a jack plate and to follow the advice in the FAQ by relocating the lower engine mounting hole to an elevated position, resulting in the engine needing to be mounted at a height of one-hole-up from lowest or possibly two-holes-up from lowest as the the lowest possible engine mounting.

With regard to how to describe engine mounting height, please read the article on that topic in the PERFORMANCE forum at

Engine Mounting Height
https://continuouswave.com/forum/viewto ... ?f=7&t=739

and also read a second article on engine mounting height at

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

With regard to getting a hydraulically operated jack plate, the much greater complexity, cost, weight, and electrical power drain of such a device seem unnecessary for this application. Typically hydraulically operated jack plates are found on boats that have very high speed potential and want to raise the engine mounting height for reduced drag when running at boat speeds of over 50-MPH, or used by anglers that want to operate the boat in extremely shallow water and will raise the engine temporarily to reduce the draft of the boat.

Your 1969 CURRITUCK 16 is 53-years-old. I don't think adding more transom weight is the best solution.

Kapharms
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Joined: Tue Mar 01, 2022 9:36 pm

Re: 1969 CURRITUCK 16 Engine Mounting

Postby Kapharms » Wed Jun 08, 2022 7:28 am

I have a 1977 SPORT 15, and I had a similar challenge when replacing my 1992 Johnson 48 with a 2022 Suzuki 50. I ended up using a 3/4-inch-thick, 4-inch-wide. 10-inch long aluminum plate.

From the back of the plate holes were countersunk for bolts to accept the new pattern on the lower mounting holes [on the new engine]. I was able to use the original blind mounting holes [apparently for attaching the plate to the transom--Moderator]. The top mounts holes were used as is.

The exact measurements and picture can be sent if needed.

Ken

jimh
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Re: 1969 CURRITUCK 16 Engine Mounting

Postby jimh » Wed Jun 08, 2022 10:50 am

Kapharms wrote:From the back of the plate holes were countersunk for bolts to accept the new pattern on the lower mounting holes [on the new engine].
Once the plate was mounted on the transom, how could you tighten the lower mounting bolts if the heads of the bolts were now in counter-sunk holes pressed against the face of the transom?

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Phil T
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Re: 1969 CURRITUCK 16 Engine Mounting

Postby Phil T » Wed Jun 08, 2022 11:38 am

Zip - It is not recommended to purchase a jackplate that adds more weight just to make up for incorrect lower holes.

This is a common situation.

The remedy is this:

Fill the lower holes with wood plugs (not dowels) slathered in epoxy.
Trim off excess plug to get flush finish to transom
Cover with Locktite marine epoxy.

Redrill lower holes using the yellow or red holes as shown on the BIA diagram. Mount the engine so that the top bolt is in the 3nd hole down from the top. The bottom bolt will be in the slot.

Image
See https://continuouswave.com/forum/viewto ... f=7&t=5808
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