Author Topic: Help on getting the right engine height on my '84 SC17 w/'04 Yamaha 115hp  (Read 199 times)

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Hi guys,

I've been reading several post and seen different setups, so I would like to know if you can help me to set the right engine height on my '84 SC17. It has a long shaft Yamaha 115hp and currently the transom screw is on the upper hole of the engine mount. I use it mostly for offshore trolling. 
1984 - 17' Sea Chaser - 2004 Yamaha 115

Online Fisherdv

Re: Help on getting the right engine height on my '84 SC17 w/'04 Yamaha 115hp
« Reply #1 on: November 04, 2019, 08:20:22 PM »
While on plane, and motor trimmed level, have someone drive the boat at cruising speed and carefully go back and look at the cavitation plate on the motor. You should just be able to see it above the water. If you cannot see the cavitation plate the motor is likely to low. How is the current performance of the boat?
2018 Sea Chaser 16, Honda 60HP

Offline Old Chaser

Re: Help on getting the right engine height on my '84 SC17 w/'04 Yamaha 115hp
« Reply #2 on: November 06, 2019, 07:46:00 AM »
I have  tried a lot of positions with my 100hpmerc and best place for me is when the cavitation plate at 1/8"-1/4" above the bottom of the (transom). It has to be at least above the transom! -too high- and it will cavitate.

Offline AJFishin

Re: Help on getting the right engine height on my '84 SC17 w/'04 Yamaha 115hp
« Reply #3 on: November 06, 2019, 10:11:36 AM »
 :yeahthat: and what Fisher described is a good way to make sure it’s set properly.

Also remember the Arima transom angles inward, so make sure your motor is trimmed down vertical when you measure and not angled against the transom.
On my Suzuki the trim had to be programmed where to stop and on my old Yamaha there was what I called, a trim stop bar that can be inserted in the appropriate hole to make sure the motor does not trim to far back. Even the slightest bit can throw everything off when you’re on the water and you trim your motor down.
« Last Edit: November 06, 2019, 10:17:41 AM by AJFishin »
1996 Sea Chaser 16, Suzuki DF60AV

R.I.P. Yamaha 70, 2 smoker

Re: Help on getting the right engine height on my '84 SC17 w/'04 Yamaha 115hp
« Reply #4 on: November 07, 2019, 05:25:09 PM »
Thanks for the replies guys, I haven't measured the performance in terms of MPG/Revs, will do that next time. One thing that always happens is after it gets on plane, and there is some wind and small waves (not rough conditions) the bow tends to go down and I have to reduce the speed as soon as I can, it has to be kind of a glass day so it can be on plane all the time. Batteries are on the transom and trims tabs are all the way up, nothing heavy on the bow.
1984 - 17' Sea Chaser - 2004 Yamaha 115

Online Fisherdv

Re: Help on getting the right engine height on my '84 SC17 w/'04 Yamaha 115hp
« Reply #5 on: November 07, 2019, 05:57:36 PM »
Are you using the motor trim?
2018 Sea Chaser 16, Honda 60HP

Online Fisherdv

Re: Help on getting the right engine height on my '84 SC17 w/'04 Yamaha 115hp
« Reply #6 on: November 08, 2019, 10:39:21 AM »
Maybe you could be a little more specific. You say the bow goes down and you have to slow down right away. Are you referring to the bow diving when coming down from a wave/following sea? Is the boat porpoising and causing the bow to dive while navigating slow, spread out rollers? Arimas being short and wide are not the best at cutting waves. Depending on conditions, many times you have no choice but to slow down. Try playing with the motor trim, and the trim tabs to see where the ride is best. Need a little more detailed info of what you’re describing.
« Last Edit: November 08, 2019, 10:55:04 AM by Fisherdv »
2018 Sea Chaser 16, Honda 60HP

Re: Help on getting the right engine height on my '84 SC17 w/'04 Yamaha 115hp
« Reply #7 on: November 08, 2019, 01:52:19 PM »
@Fisherdv yeah , that is a good description by the way, bow dives while navigating at cruise speed and there are slow, spread out rollers, some times dangerous since it dives pretty bad. There is not porpoising happening while on plane, neither bow diving when coming down from a wave since I always slow down with waves. I will try to take a video so we can discuss with more details. Thanks
« Last Edit: November 08, 2019, 01:59:59 PM by dexterloqueras »
1984 - 17' Sea Chaser - 2004 Yamaha 115

Online Fisherdv

Re: Help on getting the right engine height on my '84 SC17 w/'04 Yamaha 115hp
« Reply #8 on: November 08, 2019, 02:09:25 PM »
I think I know exactly what your talking about. It may seem counterintuitive, but try lowering the trim tabs a little, just enough to stop the bow from rising up so high. If the bow is allowed to get up too high, when it comes down over the slow rollers it will dive deep. I think the key is to control the bow with a little trim tabs so it kind of levels everything off. Give it a try at a decent, safe speed and experiment a little.
2018 Sea Chaser 16, Honda 60HP

Offline AJFishin

Re: Help on getting the right engine height on my '84 SC17 w/'04 Yamaha 115hp
« Reply #9 on: November 08, 2019, 10:51:46 PM »
In forwarding seas you gotta use your throttle just right and like how Fisher described. I like using my tabs and adjusting them just right, they’ll help make the ride a lot better. But when I’m heading into bigger swells 4’ to 6’ I go slow and quarter the swells, trim tabs are up and use my motor trim, gives me a little better control.

If I’m in a position where I have to go straight over oncoming swells, I’ll throttle down to meet the swell and then power up a little to slightly push through the swell, but not give it so much to where I slam on the backside and dig my bow in, seems to make for a somewhat smoother ride.
« Last Edit: November 08, 2019, 11:03:50 PM by AJFishin »
1996 Sea Chaser 16, Suzuki DF60AV

R.I.P. Yamaha 70, 2 smoker

Online Croaker Stroker

Re: Help on getting the right engine height on my '84 SC17 w/'04 Yamaha 115hp
« Reply #10 on: November 08, 2019, 11:01:16 PM »
Is it possible that you have a 25” longshaft outboard ?

If the prop is too deep, it will cause attitude issues. You may need a jackplate to raise it higher.

« Last Edit: November 08, 2019, 11:08:54 PM by Croaker Stroker »
1987 - 17' Sea Pacer - 2004 Evinrude 90 E-tec
15' Sea Sprinter - **SOLD**

"Ex Tridente Pax”. 🇺🇸

Offline AJFishin

Re: Help on getting the right engine height on my '84 SC17 w/'04 Yamaha 115hp
« Reply #11 on: November 08, 2019, 11:08:28 PM »
Good point CS, but his picture kind of looks like a long shaft.
« Last Edit: November 08, 2019, 11:12:35 PM by AJFishin »
1996 Sea Chaser 16, Suzuki DF60AV

R.I.P. Yamaha 70, 2 smoker

Hey guys, so I noticed two main issues by having it on the trailer during the weekend: negative power trim and cavitation plate was 1 1/2" below the bottom of the transom. Since negative power trim is a matter of adjustment while on the water, I moved to the second one just by lifting the engine to the second hole, now cavitation plate was 1/4" below the transom, then I lifted again and tried the third hole but I thought it was to much since now it was like 1/2" above the bottom of the transom, so I returned back to the second hole and put it on the water. Cavitation plate is still below the water when the boat is on plane but I don't think is too much. The swell was really good to test it, 10mph wind and small waves, adjusted the trim, trim tabs all the way up, and the boat ran really good this time, we were amazed of how a single engine lift can change the complete performance of the boat, no more dangerous bow diving, I was able to reach 14 knots and it was floating like a ballet dancer, so smoothly. We just decided to leave it as it with 1/4" bellow the transom since we mostly do offshore fishing and need torque.

Thank you all for your help!!!

« Last Edit: Today at 09:08:49 AM by dexterloqueras »
1984 - 17' Sea Chaser - 2004 Yamaha 115