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  1972 Katama, Yamaha F70

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Author Topic:   1972 Katama, Yamaha F70
Smitty posted 06-11-2014 07:18 PM ET (US)   Profile for Smitty   Send Email to Smitty  
I would like to mount a new Yamaha F70 on the transom of [a 1972 Boston Whaler KATAMA]. Can this be done without cutting thru the boat's splash well or using a jackplate? I've had a 1984 Evinrude 75 mounted on the boat using the blind holes for years. Any help would be greatly appreciated. Thanks,Smitty
contender posted 06-11-2014 10:25 PM ET (US)     Profile for contender  Send Email to contender     
I think all the hole patterns are now the same, so the engines should match up. I have a 1985 140 on my whaler, The engine sits right on the transom, I used the blind holes for the bottom in the splash well, I used bolts from the inside splash well to the engine and the upper bolts I went through the engine 1st then the transom. The blind holes (bolts) just clear the inside splash well. I do not think the Yamaha comes with blind holes on the engine mount (not sure) other wise it will not match. If you have to drill other holes (lower) in the transom for the Yamaha you will have to go through the splash well. I have heard of some people using lag bolts on the bottom into the transom wood, but I would never do this to my boat. You either can go with a jack plate, or just use the two upper bolts...Good luck
jimh posted 06-12-2014 12:48 PM ET (US)     Profile for jimh  Send Email to jimh     
Mounting engines with the standard BIA hole layout on older Boston Whaler boats with a shallow splash well is possible. The details of several methods are given in the FAQ. See

FAQ #8 How Does the Engine Mount to the Transom?

and read the material under the section, "Problems specific to Boston Whaler boats." The best workaround is the one suggested as the fifth option.

Exactly how this method will work for your boat depends on where the existing holes in the boat transom are located. If the top set of holes is properly located, you may only need to fill the old bottom holes (for the blind hole mounting) and drill a set of lower holes as described in the FAQ with a reduced spacing to the top set.

I really don't know if the existing holes from the old blind hole mounting will be useful. On some newer engine transom mounting brackets I have seen what looks like a location where a hole could be drilled into the engine mounting bracket to receive a blind-hole-positioned bolt. But I don't believe any of the newer engines actually provide that option. You might have to make your own adaptation or modification. In general, I would say it is better to leave the new engine in stock condition and make a modification to the 42-year-old boat transom, than vice versa.

Although the FAQ mentions this article and links to it, be sure to read

Boston Whaler Dealer Bulletin 10-84

to get some more ideas.

I haven't dealt with this problem myself, first-hand, and I hope you will also get some replies from other Boston Whaler owners who have resolved the same problem. They may have even more innovative methods to offer.

bloller posted 06-12-2014 05:29 PM ET (US)     Profile for bloller  Send Email to bloller     
Mount the motor as high as it can go and drill new bottom holes that will make it through to the splash well. You may be able to mount the motor one hole up from all the way up but bottom holes will be very close to bottom of splash well and washers will have to be cut nearly in half to work down there. A good SS prop should reduce ventilating
Tom W Clark posted 06-12-2014 09:35 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Yes, I agree. Mount the new F70 as high as it can go on the transom.

Abandon and fill the auxiliary or "blind" hole and drill two new holes 6.5-inches below the upper transom holes on the BIA specified lateral width.

Smitty posted 09-19-2014 02:37 PM ET (US)     Profile for Smitty  Send Email to Smitty     
Thanks for everyones advice! Motor should be installed by mid week.
Smitty posted 09-26-2014 04:08 PM ET (US)     Profile for Smitty  Send Email to Smitty     
She's done.
macfam posted 09-27-2014 07:05 AM ET (US)     Profile for macfam  Send Email to macfam     
Smitty--she's pretty!. Nice job with the F70 too. By the way, I'm heading for Katama in about three hours.
MarcB posted 10-06-2014 10:22 PM ET (US)     Profile for MarcB  Send Email to MarcB     
Very nice, those two front seats are great, looks like they would fit nicely in my 1979 Newport, where did you get them? Thanks
Smitty posted 10-07-2014 06:28 AM ET (US)     Profile for Smitty  Send Email to Smitty     
Thanks macfam! Marc those seats are original from the factory.
jimh posted 10-13-2014 09:05 AM ET (US)     Profile for jimh  Send Email to jimh     
How did you mount the engine? Did you drill news holes?
Smitty posted 10-13-2014 04:04 PM ET (US)     Profile for Smitty  Send Email to Smitty     
Jimh-Drilled new bottom holes and followed Tom Clark's suggestion[Hi Smitty -- Mount the new F70 all the way up (three holes up) which will leave about 2-1/4" of space between the top of the transom and the motor's mounting bracket. Like this:

o <-- Bolts Through These Holes

Install a 13-1/4" x 14" Yamaha Performance Series 3-Blade, Yamaha part # MAR-GYT3B-V4-14

Your top speed should be about 38 MPH at 6000-6200 RPM


Couldn't get that prop so turning 6100 rpm with a Michigan 13 1/2 x 15.

jimh posted 10-14-2014 07:37 AM ET (US)     Profile for jimh  Send Email to jimh     
Thanks for the follow-up. You followed the advice given in the FAQ as the fifth and most recommended work-around and also recommend by Boston Whaler (although they only recommended raising the engine one-hole). I see you moved the lower holes up 1.5-inches, reducing the spacing between top and bottom holes to 6.5-inches. That limits the range of mounting to be either two-holes up or three-holes up.

I think you mounted the engine three-holes up, or as high as possible. Thanks for the performance information. It is great when people share information like this, as it will help others, too.

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