Yamaha Outboard 25" vs 30" Shaft Length

[Green Mountain Grady]

Hey All,
I was wondering if someone could provide some advice as to the affect of shaft length. I have a 1991 Tournament 225 with the engine bracket that had a 1991 Yamaha 225 engine with a 25" shaft. The engine is no longer economically feasible to repair. I found a nice condition 1997 Yamaha 250 OX66, but it has a 30" shaft. Can I do a straight swap out or do I have to modify anything due to the longer shaft length? Thanks in advance for the advice!

 

[richie rich]

the engine should have multiple holes or slots so that you can adjust the overall height....you want to match the factory dimension of the prop on the water or how far off the transom's bottom edge its running....should be no big deal as long as you have 5 inches to play with, which you should. But check the distance between the mount and centerline of the prop and compare to your original and make sure it doable before shelling out the cash...having the bracket should help....I have mostly seen 20 or 25 inch shafts...30 seems a bit more rare

 

[BobP]

I think the OP is asking if he can swap lower units, using the hole pattern on the bracket isn't the right way to do it, if at all possible.

If no one here knows, ask Andy over at thehulltruth.com on the SIM forum.

 

[richie rich]

You can use any bolt hole pattern on the bracket as long as the OB engine bracket and the transom bracket remain in full vertical contact, ie no exposed OB bracket that can cantilever over. If the geometry works out, you should have room to play with. I can adjust my engine another 2-3 inches and still maintain full contact and all 4 bolt holes. It will depend on the transom brackets hole location and geometry matching up the other engine...but you have to do some math....swapping bottom ends is another story.

 

[BobP]

Grady usually mounts the motor on the 2nd hole down with the 25 inch legs , so I don't see how someone can find 5 more inches to make up with the remaining holes, that's why I say that. Some actually move the motor up to the third hole.

Unless he wants to have the leg in the water lower than necessary, than it doesn't matter.

If your suggesting redrilling the transom borings higher, I would not agree on that. If it's a bracket, can't do such a mod.

Some boats like the newer Makos use a 30 inch leg because they want the cutout up higher off the water as well as having a deeper V hull in design.

 

[JUST-IN-TIME]

you need to change over the

driveshaft
midsection only if you went to 30"
shift shaft only if you went to 30"
water tube only if you went 30"

 

[wanderer200]

I put a 25 inch on a 20 inch transom. I used brackets made by Pro-lift. They cost me 180 bucks about 3 yrs ago. Their supposed to be rated for up to 300hp. The only thing I was uncomfortable with was the increased leverage it put on the transom.
I used starboard to block off some of my transom. I used stainless L-brackets on the inside about every 2 inches. I would have made the "blockoffs" taller, but was worried the force of a good wave would blow it down. I gained 8 inches in height and did the job fairly well. The way I did it is kinda "hack-job" . I knew this boat was on the way out and needed to buy a couple years.
This is the only pic I have of the back of the boat.

 

[BobP]

Because the power is applied at the prop shaft and is much lower than the transom brackets of all outboards, when hole shooting, the top of the transom wants to be ripped off in the rear direction and the bow lift head over heals because of the torque created by that spatial separation. At the same time the bottom of the transom wants to be driven thru the boat into the bow.

If the boat manufacturer agrees (in writing) the hull can handle the higher position applied force and/or such an aftermarket product, then fine - with your insurance liability coverage too.

In this case if the device is rated 300 HP I'm sure it is and will not fail, doesn't mean what's it's attached to will not fail.

If that matters.

 

[wanderer200]

In this case if the device is rated 300 HP I'm sure it is and will not fail, doesn't mean what's it's attached to will not fail.

If that matters.

In my case, The stringers got soft and the bottom pushed in. :cry:

 

[BobP]

As long as you didn't sink and have to swim back to the dock !!

 

[awnuld]

Blocked off transom

wanderer200.

I'm interested in your 'hack job' of the blocked off transom.. I recently repowered a 25" transom with a 30" shaft and the mechanic kept mentioning how folks blocked off the transom with starboard..

I couldn't see the pic you posted..

I'm interested in the hows and why's (benefit) of doing this ?

thanks