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Drive heights

wildone

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Lower them? Or Raise them?Heard both. Any thoughts?
 

Crazyhippy

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Holy vague question batman!

On what?
Where are they now?


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wildone

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Well typically here in the us people raise motors to find their x dimension in comparison to the bottom of the boat. and yes they do gain speed, but loose handling... how ever i have heard from numerous people to lower them significantly. especially on the bigger heavier layed up boats. Guys are running 21's in au and seeing really high numbers (like upper 80's). supposedly they are doing this by drastically lowering motor heights below the bottom of the boat. not raising them. Not sure what works best, was just seeing if anyone on here had played with both before we start messing around with ours, we haven't touched it since the new motor was put on and just looking for some advice. i think i have the right prop just need to find the sweet spot.

Paging 138?
 

Crazyhippy

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Well typically here in the us people raise motors to find their x dimension in comparison to the bottom of the boat. and yes they do gain speed, but loose handling... how ever i have heard from numerous people to lower them significantly. especially on the bigger heavier layed up boats. Guys are running 21's in au and seeing really high numbers (like upper 80's). supposedly they are doing this by drastically lowering motor heights below the bottom of the boat. not raising them. Not sure what works best, was just seeing if anyone on here had played with both before we start messing around with ours, we haven't touched it since the new motor was put on and just looking for some advice. i think i have the right prop just need to find the sweet spot.

Paging 138?

the "right prop" will vary with engine height. A cleaver that flat out rips when 2" above the bottom will be a dog 2" below.

It really all about testing. Get 5-6 props, start with one and go down (or up) in 1/4" increments until it is dialed (with a skier preferred). Then move on to prop #2. Keep a log of what prop, and the changes at each engine height.

And 138 wouldn't know anything about fast boats... He just makes them pretty:p:eek:uttahere:
 

hallett21

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I would think the higher the better for speed because you are lowering the amount of drag. However too high and you've lost handling. I think you just have to do what crazy hippy suggested and just start trying props till you find what you like. Also what kind of lower unit are you running? To me I think a nose cone would naturally run better at a higher height. What your top end with your current set up? With skier and without?
 

Crazyhippy

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Under normal circumstances higher is better (usually) but NWSRA requires even with the pad or lower so really high mounts are out.

With a load behind the boat (think 2 hefty skiers) the boat might work better by getting the prop down in the water and letting it work. The gains from less wettest drive are offset by lack of propeller bite.

May also make the boat less sensitive to fuel load, rough water etc...

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138

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On our longer and narrower non air packing hulls lower in my experience has gained more speed then higher. With the new motors I have tested boats that on the high end have been 8-10 MPH the lower I have gone. It is a weird idea but it is true.
That being said if you have a boat that packs air like crazy (my Allison or a light Tunnel) do not go crazy with the over adjusting the motor down it just make the boat bow steer more at slow speeds, and high speeds the boat has to be over trimmed. Over trimming affects the attitude of the nose and killing the aerodynamics of the boat.
Test time is always the best answer for best performance in all waters. Wildone, I would bet lower on your boat would do the same as it did on my similar bottom boat. I picked up using the same 4 blade prop 8 MPH and the motor was lowered 2.75? from some starting number.?? Good luck and if I can help just call I think I will be out at LE Thursday trying a few new things out, hope they work.
 

hallett21

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On our longer and narrower non air packing hulls lower in my experience has gained more speed then higher. With the new motors I have tested boats that on the high end have been 8-10 MPH the lower I have gone. It is a weird idea but it is true.
That being said if you have a boat that packs air like crazy (my Allison or a light Tunnel) do not go crazy with the over adjusting the motor down it just make the boat bow steer more at slow speeds, and high speeds the boat has to be over trimmed. Over trimming affects the attitude of the nose and killing the aerodynamics of the boat.
Test time is always the best answer for best performance in all waters. Wildone, I would bet lower on your boat would do the same as it did on my similar bottom boat. I picked up using the same 4 blade prop 8 MPH and the motor was lowered 2.75? from some starting number.?? Good luck and if I can help just call I think I will be out at LE Thursday trying a few new things out, hope they work.

Once you lowered your outdrive what was your final prop shaft height from the keel?
 

wildone

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Crazy we have done the log and tried it all.. Time to think out the box. Hence this.


Thanks Carl that's what I wanted to hear, we have tried props and done the testing at a higher dimension and found no luck since switching gear ratios. When we ran the larger gears we got 76 with a skier and 85 with out, since switching to the fresh motor smaller gears and hydrolics the best we have seen with a skier is 70 and 80 with out. Too much wheel play at high speeds so that's the other one were going to address with prime. Been considering dropping it and seeing how it goes. Cleavers do not work on our boat. We have tried a dozen props and nothing works better then a 26p bravo or a 26p 4 blade et. The heavier hull needs those 4 blades when pulling a skier.
 
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138

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Crazy we have done the log and tried it all.. Time to think out the box. Hence this.


since switching to the fresh motor smaller gears and hydrolics the best we have seen with a skier is 70 and 80 with out.

We have tried a dozen props and nothing works better then a 26p bravo or a 26p 4 blade et. The heavier hull needs those 4 blades when pulling a skier.

Who told you to change to the smaller gears? and why? Your Hull is fine. 3 blades are fine if it is flat but just too much work keeping it on the pad in bigger water...I am a lot faster with a 3 blade but the time out of the gas to get them set after cross wash and waves is not worth it. I have a lower you can try that I think will get your numbers up. Spend some time and stop spending money on he says she says. Hay you are Bubba Army just ask? I know we can get you where you need to be. If you care for some help just ask.
 

wildone

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Who told you to change to the smaller gears? and why? Your Hull is fine. 3 blades are fine if it is flat but just too much work keeping it on the pad in bigger water...I am a lot faster with a 3 blade but the time out of the gas to get them set after cross wash and waves is not worth it. I have a lower you can try that I think will get your numbers up. Spend some time and stop spending money on he says she says. Hay you are Bubba Army just ask? I know we can get you where you need to be. If you care for some help just ask.

thanks, meant to say the larger gears. its set up the same as stevie's belgium boat but freddy is getting about 6mph more with a skier. we just cant find the sweet spot since it was re rigged and he doesnt have the time to play with it anymore.

the 3blades have hauled ass for us before i have a 26 tempest that works great except with a skier it just turns on itself and cant pull me out.
 

138

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thanks, meant to say the larger gears. its set up the same as stevie's belgium boat but freddy is getting about 6mph more with a skier. we just cant find the sweet spot since it was re rigged and he doesnt have the time to play with it anymore.

the 3blades have hauled ass for us before i have a 26 tempest that works great except with a skier it just turns on itself and cant pull me out.

Pm sent call me
 

hallett21

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Just wondering if you don't have access to an engine lift is there another way to raise and lower the motor on its mounts? For instance would the motor be able to rest on its skeg? I would think not but thought I'd ask. Or could you fill like a trash can full of towels or foam lower the motor into it and put a floor jack bellow it and adjust it that way? I have wanted to play with a few heights but wanted to avoided paying a shop every time to jack the motor up for all of 2 minutes.
 

138

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Just wondering if you don't have access to an engine lift is there another way to raise and lower the motor on its mounts? For instance would the motor be able to rest on its skeg? I would think not but thought I'd ask. Or could you fill like a trash can full of towels or foam lower the motor into it and put a floor jack bellow it and adjust it that way? I have wanted to play with a few heights but wanted to avoided paying a shop every time to jack the motor up for all of 2 minutes.

A manual jackplate would work or you can get a chery picker from Harbor Freight for less than $300 bucks and you will have it a life time.
 

hallett21

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A manual jackplate would work or you can get a chery picker from Harbor Freight for less than $300 bucks and you will have it a life time.

I've got four different mounting holes now on our Gil set back bracket. They seem to be about an inch away from eachother. Right now I am at the second tallest setting and the shaft is 2-3 inches bellow the keel

Do you think a cherry picker would be tall enough to lift a 250 opti xs?

This question got me thinking about how my boat performs. When running a high five or a bravo do you want the prop to surface or stay below water. I've always trimmed them up and let them surface a little. More so to get the nose up. I've always wondered though if I am just increasing slip and RPM and getting very little speed increase. Having the nose up helps a lot but I am not sure the prop needs to be surfacing or not.

If I were to lower the motor I could still trim the nose but would be able to possibly get more bite out of the prop. Am I correct in this line of thinking. I guess trial and error would be the best way to figure it out.
 

138

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I've got four different mounting holes now on our Gil set back bracket. They seem to be about an inch away from eachother. Right now I am at the second tallest setting and the shaft is 2-3 inches bellow the keel

Do you think a cherry picker would be tall enough to lift a 250 opti xs?

This question got me thinking about how my boat performs. When running a high five or a bravo do you want the prop to surface or stay below water. I've always trimmed them up and let them surface a little. More so to get the nose up. I've always wondered though if I am just increasing slip and RPM and getting very little speed increase. Having the nose up helps a lot but I am not sure the prop needs to be surfacing or not.

If I were to lower the motor I could still trim the nose but would be able to possibly get more bite out of the prop. Am I correct in this line of thinking. I guess trial and error would be the best way to figure it out.

Pm sent
 

Badbait

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Your boat is going to run more efficiently if you can run without possitive trim. I see a few of the skirace outboards running to much trim in my opinion. One way to check that is to park your boat on a level cement pad and with the bow wheel level the bottom of your boat. If you have a lip at the end of your pad like the Allisons do make sure you place your level forward of that lip. With the bottom level now take your prop off and level the propshaft with your trim. After you have them both level look at your trim gauge and make a mark with a sharpe showing you when your boat is at neutral trim. If you have to trim much past that mark to get your best speed you may need a little more setback or a different prop that has a little more bow lift, or possibly shifting a little more weight toward the rear. Plus you may be watering down your skiier with to much positive trim. Just my 2 cents.
 
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