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Old 28 February 2009, 15:05   #1
Country: USA
Town: Santa Cruz, CA
Length: 4m +
Join Date: Feb 2009
Posts: 11
Tech help for trimming Achilles SG140

I've given up on my local shop. They dont have any idea what they are doing so it's time I take things into my own hands.

2003 Achilles SG140
2002 Yamaha F40
SmartTab sx9510-40 Kit

Presently the motor is mounted as low on the transom as it can be. Bolted through the highest set of holes on the motor mount.

The trim angle of the motor stops (where the stop bolts go through the mount) is the also set at the lowest position.

With the SmartTabs lowered into the water so much water comes over the transom its crazy. It will swamp the boat in a couple of minutes. To me this indicates that the motor is set too low in the water?

Any kind of pointers or help are appreciated. It's worth noting that the transom of these boats isnt 90deg to the tubes. Its at a bit of an angle, so if you reference angle please indicate if that is relative to the transom of this model boat or to the centerline of the tubes.


nexus is offline   Reply With Quote
Old 03 March 2009, 10:54   #2
Country: USA
Town: Oakland CA
Length: 3m +
Join Date: Feb 2005
Posts: 6,621
Generally, if you're getting a lot of spray from the LU in the water, your motor is mounted too low.

On my late Achilles (SG-140/Honda 40hp 4-stroke; sold when I got my RIB) the motor was mounted such that cav plate was just a touch higher than the keel line. Trim was set out a couple of holes (no power trim.) I had Doel Fins on instead of trim tabs.

I also thought about putting a couple of spray shields between the transom and the tube ends, but couldn't come up with a way of fixing them. If I had it to do again, I might have some made up out of aluminum sheet and bolt them to the transom alone.



jyasaki is offline   Reply With Quote
Old 07 March 2009, 19:26   #3
Country: Netherlands
Town: Holland
Make: Brig F360S
Length: 3m +
Engine: Yamaha 70hp
Join Date: Jan 2008
Posts: 85
With an aluminium prop I'm almost sure you want:
- anti cavitation plate in-line with the sibs bottom line
- trim set to 3rd, 4th or 5th position (you will probably have 5 trim positions on a 40hp outboard, could be 4 but than again you get my idea), but that's something you can easily test by comparing with the gps in your hand. This is when you see the 1st as the lowest trim position and the 5th as the highest.

With a SST prop I'm almost sure you want:
- anti cavitation plate slightly above the sibs bottem line
- trim set to 3rd, 4th or 5th position, but that's something you can easily test by comparing with the gps in your hand.

Engine height to deep will cause (in general):
- excessive spray
- lots of drag = harder steering = most important, far less speed

Trimming low will do the following in general:
- press the bow down = less speed but easier planing

Trimming up will do the following in general:
- push the bow up = far more speed but the bow will rise sky high when going on the plane.

Now what you also want to know about this whole story is that because of a sib has flexibal contacts between the transom and the rest of the boat, trimming isn't as effective as it is with hard bottomed boats, because of the flexing around the transom that could occure and that will result in trimming won't have much effect. But with 40hp you have enough hp I think to overcome that problem.

I would say try it and you will be pleased about the results, I'm sure about that. BTW the trim-position can be easily adjusted when driving the boat, just set your engine to swallow water position and you can change the trim-position if you haven't got powertrim. If you have powertrim you can play with it when driving te boat.
reinier is offline   Reply With Quote

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