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Trimming motor up

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Dcsman59

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Trimming motor up, i’ve got a 2002 Nitro Bay 1900 tunnel. 115 mercury. Boat gets out of the hole just fine. I have to keep motor completely trim down they’ve got a jack plate on it with the motor angled even more. If you trim it up even 1/4 the prop will start cavitating. With jack plate all the way down. Have a 13 x 18 prop on it which works fine it gets up to maximum RPM for the motor. Just don’t understand ?I can’t trim the motor up. To help bring the bow up out of the water at all.
 

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Larry Williams

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I'm no expert on this topic but here are my thoughts.....
Tunnel hulls have that "tunnel" cavity at the rear pad area to direct water up to the prop to run in very shallow water. That water is much disturbed approaching the propeller. This hull designs produces very little bow lift since that is not its designed function. A flat wet ride is common in rough water. That said you might be able to improve it some with proper engine height and prop configuration. If I'm seeing the picture correctly, you haver a couple of spacer wedges at the top of the mount that seem to be tucking the motor under. That works against lift unless you could trim the enging back a lot. Those could be removed maybe?
 

jerry shack

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I'm no expert on this topic but here are my thoughts.....
Tunnel hulls have that "tunnel" cavity at the rear pad area to direct water up to the prop to run in very shallow water. That water is much disturbed approaching the propeller. This hull designs produces very little bow lift since that is not its designed function. A flat wet ride is common in rough water. That said you might be able to improve it some with proper engine height and prop configuration. If I'm seeing the picture correctly, you haver a couple of spacer wedges at the top of the mount that seem to be tucking the motor under. That works against lift unless you could trim the enging back a lot. Those could be removed maybe?
Hey Larry,
I think you are going the wrong way . if he can't trim at all he would need more negative trim. That's why the motor has wedge blocks. I would lower the motor down to the last hole on the jack plate to get more bite and take the prop to a prop shop and have them put in a super cup on it for surface piercing it might take away 100-200 RPM's . Just saying
 

Larry Williams

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Jerry, I'm seeing that the negative trim (prop tucked under) is pusing the bow down. Good for a quick launch out of the hole but then trimming up to raise the bow is somewhat offset by the negative allignment with the wedges?? I'll be the first to agree that this stuff is above my pay grade. Ha. I do agree that lowering the motor is the first thing I would try..... I've used the SE 300 hydrofoil with great success and I would have to put one on this rig for sure.
 

Kirby Wilson

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This boat is a 2400 LB boat over 19 ft long and 99 inches wide. A heavy boat for a 115 hp motor. Not much experience with hydrofoils only test run Stratos hydrofoil for a day in the late 80s. They are design to allow the motor access less turbulent water with a higher motor height. The ride is different also tends to bounce side to side. The boat didn't have a lot of bow lift just total boat lift when trimmed.
 

Dcsman59

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I would like more horsepower myself. Looking for a 150 for it now. The 115 has a 20 inch shaft. Wondering if 25 inch shaft might work better for trimming up, to get some bow lift . You can trim this setup much at all.
 

Dcsman59

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Jerry, I'm seeing that the negative trim (prop tucked under) is pusing the bow down. Good for a quick launch out of the hole but then trimming up to raise the bow is somewhat offset by the negative allignment with the wedges?? I'll be the first to agree that this stuff is above my pay grade. Ha. I do agree that lowering the motor is the first thing I would try..... I've used the SE 300 hydrofoil with great success and I would have to put one on this rig for sure.
Going to try Lowering the motor first! I’m gonna have a super cup on the prop.and add hyrdofoil too !
 

jerry shack

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Going to try Lowering the motor first! I’m gonna have a super cup on the prop.and add hyrdofoil too !
There is one thing we are missing after I looked at the photo again, and that is the Lenco trim tabs. To me they look like there are not up all the way or are installed to low on the transom. That would most defiantly make that boat have no bow lift. As I see it some one was having a hole shot problem that's why trim tabs and neg. trim wedges they add 3-4 degrees of neg trim. I would take a straight edge and put it flat on the hull and see how much area there is between the bottom of the tab and the straight edge. There should be about 3/4-1" just saying.
 

Larry Williams

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Jerry,

Good observation.

Dcsman59- I should have noted that you canNOT use the SE 300 hydrofoil with the trim tabs. It has to be one or the other but never both. I hadn't noticed the trim tabs when I looked at the picture- sorry. I would think that on a bay boat the trim tabs would be best- if propery functioning. I will say that on my Z-18 the SE 300 hydrofoil was the single best performance inprovement that I made. about half the world says they are no good but I have to disagree. hole shot with any load only requires 3,000RPM that can be applied gradually anytime. I'm sure I've saved a lot of gas using it and have no negative issuess with it. I run the Atlas hydraulic jack plate and it has the added benefit of allowing a higher running position without losing water at the prop.
 
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