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Help on getting the right engine height on my '84 SC17 w/'04 Yamaha 115hp

Started by dexterloqueras, November 04, 2019, 07:57:07 PM

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dexterloqueras

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

Fisherdv

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 BFP60

Old Chaser

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.

AJFishin

 :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.
'96 Sea Ranger 19, 2016 Mercury 115 EFI CT (115F231D) 
'96 Sea Chaser 16, 2019 Suzuki DF60AV (Sold) 
'87 Sea Chaser 17, 1987 Johnson V4 90 (Sold)
My YouTube channel: youtube.com/socalseachaser

dexterloqueras

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

Fisherdv

2018 Sea Chaser 16, Honda BFP60

Fisherdv

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.
2018 Sea Chaser 16, Honda BFP60

dexterloqueras

@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
1984 - 17' Sea Chaser - 2004 Yamaha 115

Fisherdv

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 BFP60

AJFishin

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.
'96 Sea Ranger 19, 2016 Mercury 115 EFI CT (115F231D) 
'96 Sea Chaser 16, 2019 Suzuki DF60AV (Sold) 
'87 Sea Chaser 17, 1987 Johnson V4 90 (Sold)
My YouTube channel: youtube.com/socalseachaser

croaker stroker

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.

1987 - 17' Sea Pacer - 2004 Evinrude 90 E-tec
1985 - 15' Sea Sprinter - **SOLD**

"Ex Tridente Pax". 🇺🇸

AJFishin

Good point CS, but his picture kind of looks like a long shaft.
'96 Sea Ranger 19, 2016 Mercury 115 EFI CT (115F231D) 
'96 Sea Chaser 16, 2019 Suzuki DF60AV (Sold) 
'87 Sea Chaser 17, 1987 Johnson V4 90 (Sold)
My YouTube channel: youtube.com/socalseachaser

dexterloqueras

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!!!

1984 - 17' Sea Chaser - 2004 Yamaha 115

dexterloqueras

Quote from: dexterloqueras on November 11, 2019, 09:00:26 AM
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 too 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!!!
1984 - 17' Sea Chaser - 2004 Yamaha 115

AJFishin

That's good to hear, but your motor looks to be trimmed down to far forward, but it could just be the way the picture is in comparison to the sponsons angle.
With your boat sitting flat in the water, your motor should be parallel with the boats waterline, not down against the transom. This will cause your bow to plow in the water too.
My new Suzuki's trim angel is programmed by using the controls, where my old Yamaha had a trim limiter bar.

This picture shows an incorrect trim setting.


'96 Sea Ranger 19, 2016 Mercury 115 EFI CT (115F231D) 
'96 Sea Chaser 16, 2019 Suzuki DF60AV (Sold) 
'87 Sea Chaser 17, 1987 Johnson V4 90 (Sold)
My YouTube channel: youtube.com/socalseachaser

crabby

My Yamaha 4 stroke the plate is above the bottom of the boat I'd guess 1/2 - 3/4. It's up as high as I have bolt holes. It's a 20" shaft. On an ideal day I can tickle 35 mph. Ok that's not ideal for cruising motor trimmed up right as well. Normally cruise @ 4000 ish about 25 mph. I've got a 15x13 3/4 Yamaha AL prop. With the weight of the motor my stern well seems a bit comprised so I cut out a app. 3.5" piece of 1/2" starboard to stop some of the splash from the ster from dumping the well.

Fisherdv

Quote from: crabby on November 18, 2019, 06:16:25 AM
My Yamaha 4 stroke the plate is above the bottom of the boat I'd guess 1/2 - 3/4. It's up as high as I have bolt holes. It's a 20" shaft. On an ideal day I can tickle 35 mph. Ok that's not ideal for cruising motor trimmed up right as well. Normally cruise @ 4000 ish about 25 mph. I've got a 15x13 3/4 Yamaha AL prop. With the weight of the motor my stern well seems a bit comprised so I cut out a app. 3.5" piece of 1/2" starboard to stop some of the splash from the ster from dumping the well.
Crabby, what size boat and motor do you have? From looking at your signature pic that motor looks huge.
2018 Sea Chaser 16, Honda BFP60