Performance Question

[OkieHenry]

I have a 1977 Terry ABF 15.6 ft bass boat With a 1977 85hp Johnson, Its rated for a 90hp, I have thought about adding a jackplate, Will this help my boats performance? and if it does help the performance would a 12" jackplate be to much.

 

[tashasdaddy]

Re: Performance Question

it might and it might not. moving back moves center of gravity. i would try to get the best set up you can with out it. proper engine height on the transon, proper use of trim. balanced load in the boat.

 

[OkieHenry]

Re: Performance Question

ok thats what i wanted to know thanks, Is there anything I can do to get some more top end?

 

[bktheking]

Re: Performance Question

ok thats what i wanted to know thanks, Is there anything I can do to get some more top end?

What prop pitch are you running on the motor?

 

[OkieHenry]

Re: Performance Question

some one told me it was a 13-1/2 19 pitch, the only marking on it is PJ-84

 

[Tacklewasher]

Re: Performance Question

Best thing to do is to make sure the boat/motor/prop is set up right.

Do you have a tach in the boat? And do you have access to a GPS? Knowing your WOT rpm and speed will tell us a lot about your current setup and if it can be improved on by set up and prop.

Some things I have done to get better performance were raising my motor to the top hole and moving the weight around in the boat as well as going to a lower pitch than I thought I would need (15p).

Without a tach and gps, you really can't figure it out.

 

[TN-25]

Re: Performance Question

At full throttle you want your motor to operate within the rated full throttle rpms that it is rated for. If it is below the rated maximum operating range rpms, you are not making all the power the motor is rated for (it might be overpropped, the motor may be set too low in the transom, the prop may be out of spec and need trueing, the hull might be cupped, load needs to be balanced, waterlogged boat flotation, or any host of other engine ailments...). On the other hand, if you have the motor underpropped (i.e. too low of a pitch) you could destroy the motor by over-revving.

 

[Dhadley]

Re: Performance Question

I wouldn't worry too much about "over-revving" on that motor. The port timing is pretty low and the port area is pretty small. At any rate the stock steel reeds will give up around 6200-6400 - if the port timing let it get that far. That's without even considering the small carbs.

I'd still shoot for 5800-6000. That gearcase isn't the sleekest but there are things you can do. Anyway I'd get a good solid baseline and go from there. A jackplate probably isn't going to do you much good with that prop. Just not a lot of technology there even if it's new.

With a good prop a jackplate will probably help but I'd be willing to bet that 12" is at least twice what is optimum on a 15 1/2' boat.

 

[OkieHenry]

Re: Performance Question

Ok I have been busy, I did pull my prop it's a 15 pitch 13-3/4, at this time my tach don,t work the needle goes all the way to the right when I start the motor, now let me explain about the prop This is the first boat I 've ever owned and I have very little knowlage about boats

Around July this year a kid around 17 came in the bait shop where i work and ask if I knew of anyone looking for a boat to make a long story short, with his parents pemission I gave $400 for boat, motor, & trailer

I took the boat to a buddies house and he got it running, we took it to the lake and it wouldn't plane out, got it home and my FIL wanted to here it run, and of coruse it would not start, we figured out it needed a new stater and a prop so I bought another motor same year and eveything "so I thought" Got it running, put on the other prop and it does about 35mph at full throttle
now that i pulled the prop off I can see the differance the one that was on the boat when I got it is a Michigan PJ84 and some one told me it was a 19 pitch 13-1/2 but I don't know

So I am going to get this prop rebooted and try it a guy told me I should get another 10mph going from a 15 pitch to a 19 pitch

 

[emdsapmgr]

Re: Performance Question

You've gotten some excellent comments. Until you get your tach fixed, you won't be able to tell where you have been vs. where you are going-performance wise. Top speed is just part of the story. Each time you go out, take a notebook and make notes on rpm's and related speed. It's a trial and error approach and your notes will help.