Motor Height

[knouse94]

I have a 15.5ft 1970 Venture bass boat, with a 1978 70hp Johnson. I am wondering if the motor is to far in the water. The motor height seems to low to me. I was wondering how this would effect my performance. I can move the motor up if needed. The motor sits about 4 inches under the boat. Thanks

 

[V153]

Re: Motor Height

With your rig I'd guess you could easily run at a moderatly elevated height. If the motor's sitting directly on top of the transom that's way too low. Assuming the shaft length is correct for the hull that is. If it were me I start with the cav plate at least even with the keel, mebbe 3/4" higher, and see what happens.

I ran a full 2" above the keel with a 90 on my 15'3" Glastron. Only problem I ever had was if I was running really hard flat out for more than say 5 minutes. I'd get a high temp alarm. And that only happened in the heat of summer when the water's real warm.

Note: If you start getting up there you might wanna look into a semi-surfacing prop aka chopper. Good luck!

 

[Solittle]

Re: Motor Height

Motors sitting 4" under the boat usually do not run well.

 

[Bob_VT]

Re: Motor Height

Where are you taking the measurement from??? It need to be taken from the plate directly above the prop and with a straightedge to the keel.

 

[V153]

Re: Motor Height

Motors sitting 4" under the boat usually do not run well.

Ya, makes it hard to get air into em ... Heh heh heh

 

[V153]

Re: Motor Height

Measure like so:

 

[knouse94]

Re: Motor Height

Thanks for the info guys I will try to raise the motor and see what happens. I am assuming this is the problem with my performance. I am only running between 25-30mph and the motor runs great. I thought I would be closer to 40mph with a 70hp on this small of a boat. Thanks

 

[V153]

Re: Motor Height

I thought I would be closer to 40mph with a 70hp on this small of a boat

I would reckon so too. What kinda prop are you swinging. Do you have a tach? Is the boat soggy?

 

[knouse94]

Re: Motor Height

Right now I have a 13-3/4" x 15 prop on there. The guy that had this motor before me had it on an 18ft aluminum v-hull with a 12-3/4" x 19. I have seen no foam in the boat and I can be out for 5 hrs and my pump will not kick on. I do have a tach but I cannot get it to work. I have one other option I need to try on it and hopefully that does it. I have a 15, 17, 19 pitch props. I am going to raise the motor and try them out to see what happens. Thanks