Prop Help

[Paul12]

Anyone out there work in the Outboard motor business? I bent my prop and need to get a new one, but before i buy one I want to verifiy that it is the correct size for my boat/engine. It is the original prop that came with the outboard and boat. The dealer said it was factory matched, but he also said I should be getting about 5-8 mph more than I am.

[Starfish]

I don't work in the outboard business, but the first thing you're going to need to be able to tell someone is what boat, motor, and prop you're currently running and how many RPMs and miles per hour you're getting at WOT (wide open throttle). How well your boat is performing coming out of the hole, making tight turns, and whether it has any problems with porpoising are also worth noting. If you want to get even more refined, take a look at where your outboard is bolted on the boat so you can tell them which hole it's mounted in (i.e. is there room to adjust the motor upward or downward on the transom) and where the cavitation plate sits relative to the bottom of the boat.

"Factory matched" is kind of a misnomer for boats, since the factory has no way to know what elevation you're running your boat at and how heavy of loads you're carrying. "Boat shop matched" would be more likely to succeed, as long as they had quizzed you about what your performance goals are and how you will be using the boat.

[Paul12]

I have all that info. The boat is a 2003 Tracker Targa. the motor is a 2004 Mercury ELPTO 60HP outboard. The prop currently on it is 10.88 x 11. The RPM at WOT is 5500 and speed is 24 knots. Coming out of the hole is ok but not exceptionaly great. Turning is really good and I have no problems with porposing, but to get to the top speed of 24knots, i have to trim the motor at least halfway up. The dealer and a service tech I had talked to quite awhile ago both said I should be getting about 32-33 knots for speed. The boat weighs 1700lbs. the outboard is mounted on the top set of holes and there are 5 sets of holes total. The cavitation plate is even with the keel of the boat. I don't have the money to buy different size props to find the right one. i am hoping for help to find out if a slightly different pitch will help me out or if I should stay with what I have.

[ICHTHYDEMON]

Trimming the motor up isn't a bad thing,it gets more boat and motor out of the water and with that you'll get better handling and more speed.

Typically trimming the engine up to where it starts to porpoise and backing down a bit will net the fastest speed. I don't know that you'll get to 32-33 with just a 60. Is the boat 1700 dry or is that loaded with gear and fuel?

I have a feeling that the engine is mounted too low. Even with the keel is a good starting point for the cavitation plate,its probably not optimal. You might want to raise the engine a notch at a time and see what happens.

[Starfish]

:yeahthat:
At first glance it sounds like your boat is a bit underpowered, but I would expect a little more speed than that. You didn't mention, how long is the boat?

5500 RPMs at WOT doesn't sound like a bad match for the prop. I'd try raising the motor up a couple of holes. If you're mounted in the top holes you should actually have some room to adjust the motor upward-- the top holes mean it's all the way down. Your RPMs will come up a few hundred and hopefully you'll pick up a few miles per hour.

As Ichthy stated, trimming up your motor helps pick more of your boat up out of the water and will increase your speed. Keep trimming until you either porpoise or the prop ventilates, then back off a little for best performance.

Good luck!

[trap50]

:yeahthat: Just remember if you start to cavate on turns or just going straight lower the motor so you don't burn a prop.

[ICHTHYDEMON]

I looked at the Tracker line and as far as I can see you must have the 16' Targa. Its the only Targa that Tracker puts a 60hp on.

Tracker states that the top speed will be 28-31. It sounds like you're not too far off.

[Paul12]

I have the Targa 17 WT. I need to repower it but I don't have the moeny right now. 1700 lbs is loaded weight. and i weighed it last night at a local scale while loaded. it is 1647lbs. I am kind of afraid to raise the motor a few sets of holes. the boat has a very shallow draft and the motor looks as if it should not be up any higher when the boat is in the water. Should the cavitation plate be higher than the bottom of the keel of the boat? Thanks for this info guys, this is a subject I do not know much about.

[ICHTHYDEMON]

Should the cavitation plate be higher than the bottom of the keel of the boat?

Mounting the engine with the cav plate even with the bottom boat is a GENERAL rule of thumb. The more shaft in the water,the more drag there is. More drag=less speed. You can raise the motor too much though. Thats why I recommend a hole at a time.

Dealers set boats up this way because they're lazy. Its easy to set the motor on the boat drill a couple holes and call it a day. They generally aren't doing the customer any favors this way.

A 60 isn't heavy enough that you can't raise it at home. Have a couple buddies help you raise the motor a notch and do a water test. You'll know you've gone too high if the prop blows out when accelerating or when you make a turn. Be sure to watch the telltale as well,you don't want to lose water pressure.

If it still runs without cavitating bring it home and repeat.

I can almost guarantee you'll gain rpms and more speed.

5500rpms is the very bottom of the rpm range for that motor,you should be closer to 6000.

Raising the motor will net more rpms and a prop change (less pitch) will as well.

[Paul12]

Thanks, i will try that. If I stay at the mounting holes it is at, is there a prop pitch I should go to? Say instead of 10 7/8 x 11 go to a 10 1/2 x 12 or 13?

[ICHTHYDEMON]

Thanks, i will try that. If I stay at the mounting holes it is at, is there a prop pitch I should go to? Say instead of 10 7/8 x 11 go to a 10 1/2 x 12 or 13?


Don't go to any more pitch,more pitch will lower rpms even more.

Going to a 12" pitch will lower your rpms about 150-200. Going to a 13" will net you another 150-200rpm loss.

You need to gain rpms not lose them.

[Paul12]

Ok. Thanks

I borrowed a prop that is the same size and model as mine from my neighbor and tested the boat again. At Wide Open Throttle I was getting about 5700-5800 RPMs. So now I have a more exact RPM to go off of.

[ICHTHYDEMON]

Where are you getting the speed numbers from? GPS or speedometer?

[Paul12]

Both. they show the same speed. The speedometer I have is digital.