CMC Manual Jackplate and Prop height

[ctf58]

Hello fellas,

Got a new to me boat. 1998 BassCat Sabre with a 150 Merc EFI.
It has a 4 blade 24 pitch Trophy SS prop, CMC Manual Jackplate 6" setback and a StingRay III hydrofoil.

The guy I got it from knew nothing about boating at all. Lucky for me he also never drove the boat, he had a friend drive. Secondly he only took it out a couple of times in the past 5 years and the boat only has 75 hours on it. He put the foil on it because he heard they helped with fuel consumption.

Anyway, When I test drove it the water was very rough but the boat did great. Yesterday I got it out for the first time on a good day of water. Boat is fast.

But, up in plane I think I heard the prop ventilating under the foil. I do not need any more speed and plan on taking the foil off to see what that changes.

Where do I start on the height of the jackplate? I've read several post and my head is swimming.

I can really hear it ventilating in sweeping turns and can see alot of spray coming up in front of the foil on the passenger side of the motor. Roostertail is none existent because of the foil.

I think the prop is to high and my RPM's are 5900 WOT at 65 MPH.

Questions are:
1. What should WOT be on a 1998 Merc 150 EFI?
2. Where to start on the jackplate height or how much should I start lowering it 1"-2" ?
3. Hydrofoil on or off until I get smart tabs? When I get the money Smart Tabs will be ordered probably next year.
4. What have I got myself into?

P.S. 5900 WOT at 65 MPH was a full tank of gas (32gal) 3 batteries and 2 people.

Thanks in advance, you have helped a lot in the past!

 

[SparkieBoat]

Re: CMC Manual Jackplate and Prop height

hydro foil is fine and will help stop ventilating. I raise my motor up till the hydro foil is just out of the water at WOT and trimmed out, it may vent slightly in hard turns at WOT, but I dont make hard turns at WOT, I slow down. It sounds like you have a perfect set up to me. Raise the motor to the point of just before venting, basically the higher you can get your motor the better. when you say you can "hear" it venting, do you mean the RPMs shoot up without a speed increase???

 

[ctf58]

Re: CMC Manual Jackplate and Prop height

hydro foil is fine and will help stop ventilating. I raise my motor up till the hydro foil is just out of the water at WOT and trimmed out, it may vent slightly in hard turns at WOT, but I dont make hard turns at WOT, I slow down. It sounds like you have a perfect set up to me. Raise the motor to the point of just before venting, basically the higher you can get your motor the better. when you say you can "hear" it venting, do you mean the RPMs shoot up without a speed increase???

when I say I can hear it. I mean that I can hear it from the prop. no real increase in rpm's.
thank you for the reply.

 

[ctf58]

Re: CMC Manual Jackplate and Prop height

are my rpm still too high it wide open throttle? 5900 seems too high. if I lower the engine will the rpm's go down and get better hole shot?

 

[WHITENOISE]

Re: CMC Manual Jackplate and Prop height

Your setup sounds pretty good to me. 65Mph out of a 150 merc. is pretty respectable. I think what you are hearing is the prop exhaust. At WOT that sound is normal on a raised motor. 5900 RPM is near max but not 2 much. I never run more than a mile or two @ WOT anywhay.

 

[SparkieBoat]

Re: CMC Manual Jackplate and Prop height

do not lower your motor if it is not venting...if anything go higher. but it sounds like it is good. if it vents your RPMs will spike with no speed increase. if you want better hole shot get a set of trim tabs. 5900 is good for WOT, I usually back my throttle off to around 5000-5500 for better fuel mileage.