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Old 15 April 2021, 01:40   #1
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Country: USA
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Setting correct height for Tohatsu 9.8 (Video)

Hey everyone! So I did quite a bit of testing yesterday with my Tohatsu 9.8 and Saturn inflatable. I feel like I'm getting closer, but I have a few concerns. Decided to just start a new thread since the discussion has progressed beyond the main topic of the old one. I hope that's okay with everyone .

Just for reference, transom is 15 inches and measurement from engine clamps to anti-cav plate is 17 inches. The result without shims is producing way too much spray. By the time I get back and take off the engine cowl, the valve cover is just covered in salt residue. It's not too bad to clean off, but I imagine this won't be good for the engine long-term.

So here is the testing video! Did this in Sarasota Bay and Roberts Bay which got a bit choppy by the time I got to 3 shims, so couldn't go full throttle in the last test.



With 1 shim, I was getting a little splashing around the engine and full throttle kicked up a ton of splash. With 2 shims, the splashing around half was reduced but full throttle still had tons of splash. With 3 shims, I got less splashing overall, but couldn't test full throttle. Unfortunately, I'm not able to go higher than 3 shims since the clamps are on the upper lip of the inner transom plate.

Is the full throttle spray normal? I was uneasy with 2 shims, but 3 shims really had me worried the motor would come loose. If I can get away running with 2 shims, that's what I'll probably do. Also when running with 2 and 3 shims, I had a strange rattling sound coming from the transom. Still trying to figure out what that was.
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Old 15 April 2021, 02:41   #2
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I think Loco's old guide would help - full of info:

https://www.rib.net/forum/f50/abc-si...nes-58373.html
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Old 15 April 2021, 11:14   #3
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Loco did a monster write up there which did suffer a little from why use ten words when you can use a hundred... something I try and keep in check... just!

So in my experience it's...

Make sure you are up to pressure on tubes/keel & recheck after a few mins on the water.

Get the boat trimmed level by weight distribution... if solo unless carrying a week's camping kit at the bow you'll need a tiller extension to move your weight forward.

Set the outboard trim pin so the AV plate is parallel with the water when on the plane... hopefully this will be one of the more central trim pin positions.

Use increasing packers (as you've done) until the splash reduces to nothing or at least an acceptable amount. If you have reached the safe limit for the clamps still with massive splash and you're not yet getting prop ventilation (slip) issues then you need to go higher with a proper transom lift. Make this a bit higher than you might need constructed in such a way if it is too high and the prop ventilates it can easily be reduced bit at a time.

Two observations... as I've already said this outboard leg design was the most splashy I've ever owned... also it may be camera lens distortion/angle but it did look as it you were running stern heavy and with the outboard pin too near the transom.

My own transom lift to reduce splash on this engine type is here posts #69-#78...

https://www.rib.net/forum/f50/aerote...e-71528-2.html
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Old 15 April 2021, 12:35   #4
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Quote:
Originally Posted by Fenlander View Post

Two observations... as I've already said this outboard leg design was the most splashy I've ever owned... also it may be camera lens distortion/angle but it did look as it you were running stern heavy and with the outboard pin too near the transom.
Completely agree, I don't see the shims adding much, that outboard transom angle looks to severe. Adding a bag of sand up front and making sure the inflatable boat pressures and keel are spot on.

Used to run a Zodiac GT with 25hp 2-stroke which was like poetry in motion with 2-up once on the plane, with virtually next to no splash back, plus you could ease off the throttle and cruise and just see the top of the anti-cavitation plate.

As mentioned - adjust the trim angle on the outboard.
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Old 15 April 2021, 14:14   #5
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Yep stern heavy I think too, water inside the cowl shouldn’t happen either
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Old 16 April 2021, 12:22   #6
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Quote:
Originally Posted by Max... View Post
I think Loco's old guide would help - full of info:

https://www.rib.net/forum/f50/abc-si...nes-58373.html
Thanks for the link Max! I learned quite a bit from that guide.

Quote:
Originally Posted by Fenlander View Post

Set the outboard trim pin so the AV plate is parallel with the water when on the plane... hopefully this will be one of the more central trim pin positions.

Use increasing packers (as you've done) until the splash reduces to nothing or at least an acceptable amount. If you have reached the safe limit for the clamps still with massive splash and you're not yet getting prop ventilation (slip) issues then you need to go higher with a proper transom lift. Make this a bit higher than you might need constructed in such a way if it is too high and the prop ventilates it can easily be reduced bit at a time.

Two observations... as I've already said this outboard leg design was the most splashy I've ever owned... also it may be camera lens distortion/angle but it did look as it you were running stern heavy and with the outboard pin too near the transom.

My own transom lift to reduce splash on this engine type is here posts #69-#78...

https://www.rib.net/forum/f50/aerote...e-71528-2.html
Thanks for the advice! That transom modification is really neat!

I should have included this photo initially, but here is the way I was running the boat in the video. It's at the third hole out from the transom which makes it seem pretty level with the rest of the boat (not the keel though). Next time, I'll run it at the fourth hole out. Unfortunately, I can't remove the pin when the motor is mounted due to a bad decision of mine when locating the transom wheels.

Just a thought, but trimming the motor higher than this won't cause any bad tendencies right? I've always feared a wind gust getting beneath the bow and giving me a view of the sun.



Quote:
Originally Posted by spartacus View Post
Completely agree, I don't see the shims adding much, that outboard transom angle looks to severe. Adding a bag of sand up front and making sure the inflatable boat pressures and keel are spot on.

Used to run a Zodiac GT with 25hp 2-stroke which was like poetry in motion with 2-up once on the plane, with virtually next to no splash back, plus you could ease off the throttle and cruise and just see the top of the anti-cavitation plate.

As mentioned - adjust the trim angle on the outboard.
Will double check pressures out on the water. I do have my fuel tank and gear in the bow, but don't have a tiller extension so I'm just aft of the mid point. I just set up a chair mount and will order a tiller extension so I can get the weight more forward.

Quote:
Originally Posted by jeffstevens763@g View Post
Yep stern heavy I think too, water inside the cowl shouldn’t happen either
Wow I always thought that water in the cowl was normal. I'll speak with the motor dealer and see if it can be looked at under warranty.
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Old 16 April 2021, 12:45   #7
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Great feedback... really helps.

I think you have to try a tiller extension so you can move your own position even further forward as a trial.

Re the outboard trim pin the photo isn't 100% clear but it seems you could try one more hole out.

Re the water under the cowl this is being pushed into that area because your splash is really excessive... not a motor fault. As I've said before just what happened with my Mariner version of the same engine until I made that higher transom modification.
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