Boat set up

[timdan94]

I have a 1985 85 hp force outboard on a 15 ft mfb caprice. 650lb hull, 300ish motor, plus gear. I have a 13x17 prop on it I can trim all the way out without the prop blowing out. Is my motor set too deep or do I need a bigger prop? I can get 5600+ rps out of it with me, my gf, fishing gear, and 12 gallons of gas.

 

[tashasdaddy]

Re: Boat set up

5600 is a good place to be. AV plate should be 1 inch above keel.

 

[timdan94]

Re: Boat set up

here are a few pictures of how my boat is set up now...

 

[Bob_VT]

Re: Boat set up

You might be able to go up a notch but your control will suffer and it might only afford you 1-2 mph more. I would trade off the fraction of speed and keep the control.

 

[Frank Acampora]

Re: Boat set up

Go up an inch by moving the bottom bolts to the lower hole, then get a 13 X 19 prop. 5600 is 100 over the operating range. It will not hurt anything but a 19 pitch will drop you to about 5200 which is closer to the middle of the 4500-5500 range. loosen the top clamps, remove the bottom bolts and use a pry bar under the mounting clamps. Temporarily put in wood blocks to hold the engine up then re-bolt the bottom and tighten the top. There is no need to fill the 1 inch gap above the transom. Whole job should take 15 min to 1/2 hour.

With that slight flat riding pad at the bottom of the transom, you may experience some ventilation/cavitation but a cupped prop will help. Also, try to find the black plastic "Flare Washer" that fits on the prop under the nut. It is about 4 inches in diameter and an inch thick, tapered. It helps with the hole shot. However, you may find as I did that you still will be able to use full out/up trim.

I have my 90 on a 15 foot Glastron and she gets 43 MPH GPS at about 5200 RPM with a 13 X 19 stainless prop. She is jacked an inch and I do not get any cavitation on the hole shot or during cruising. I do ventilate a bit in relatively sharp turns--that is, turning in a 500 foot wide river. As a matter of fact, my Glastron does not like any in/down trim and becomes very squirrely. She even likes to do the hole shot with full up trim.

 

[timdan94]

Re: Boat set up

I have this prop that I got repaired that is a 13x19 how do you know if it has cupping or not? The numbers on it are 686265

 

[Frank Acampora]

Re: Boat set up

That's a stock Force semi-cleaver prop. It is not cupped. Personally I do not like them and if I buy an engine with one, I sell the prop as quickly as I can. It is an open hub prop and was designed for the newer Force dual exhaust lower units.

I do not think they perform as well as a stock Chrysler prop or the Michigan branded prop. If it were mine, I would sell it on ebay and buy another.

However, I do not have hard numbers to prove my feeling. You may find that you like it and get adequate performance. Note that all the props I have mentioned including the semi-cleaver are manufactured by Michigan but each has a different hub and blade design.

Some of the Michigan stainless props are already cupped but I think the aluminum ones are not. A prop shop can cup any prop for you or you can do it yourself. Cupping is a turning in of the trailing edge of the blade and helps the prop "grab" the water better. It does not increase speed except that sometimes you can run the engine or trim higher for less drag thus more speed. Cupping will most likely reduce RPM by about 400 so in that respect it has the same effect on RPM as going up 2 pitches in prop.

If you want to look for some props, send me your email in a private message and I will send you a couple of demo-photos of props and the flare washer.

I am on Vista and have not yet learned how to get photos small enough to post here.

By the way: Your depth finder transducer seems to be too high. Usually (if they also have a speedometer) the bottom is supposed to ride about 1/8 to 1/4 inch under the water when the boat is moving on plane.

 

[timdan94]

Re: Boat set up

I think I will try the prop just to see if it works seeing I already spent $66 on repairing it. If it doesn't do you know how much to ask for it?

 

[timdan94]

Re: Boat set up

the transducer only has temp on it. the fishfinder has gps so I'm hoping I can get away with it there. if not I can lower it about a 3/4" to an inch.

 

[timdan94]

Re: Boat set up

I just got to testing that 13x19 prop and I only lost 100 rpm and I gained 1 mph. I'm now running 36 mph at 5200 rpm. I used this web site and it says I have 24.50% slip which doesn't seem right.