Prop pitch question

[djrascoe]

Im not sure what to go with, any help is appreciated. I need to get a different prop for my boat, but I have no idea what pitch to get. It currently has a 11 pitch on it, and from what ive read on here, its not right for my boat. The boat is a 77 sliverline kodiac 17 foot tri hull with a 77 mercury 1150 outboard on it. I think the boat is about 850 - 900 pounds with the motor. Im basically looking for the best speed i can get, but at the same time id like to reserve a little on fuel. I plan on using it to fish, and occasionally pulling the kids on a tube. What pitch prop do you suggest that i go with?

 

[IamCanadian]

Re: Prop pitch question

Speed and RPM would help ALOT, But I think a prop in the 14ish range would work ok. 11p props are used on 35-45 hp motors.

That is Just a guess I do not own a 115hp outboard.

 

[jestor68]

Re: Prop pitch question

I would ditch that pontoon prop and start with a 17" pitch on that boat.

It might pull a 19" (if the motor is healthy) with a light load, but the 17 would serve you better for pulling anything with the minimum of two people in the boat.

Using a tachometer, the rpm at WOT to shoot for is 4800-5300 rpm.

 

[Georgesalmon]

Re: Prop pitch question

It is really important to know what WOT rpm you were getting with the 11" pitch prop. Guessing is not good enough if you want to keep your motor running for a while. 900 lbs sounds very light for the boat you described. I'm running a 15p 4 blade on a 1979 1150, and my boat is 20' and over 3000lbs. But the pitch of the prop on my boat won't relate to yours even though the engine is the same, each boat is different.

 

[djrascoe]

Re: Prop pitch question

I messed up when I put the weight, from what im reading on the year and model, its 1850 - 1900lbs. Im not sure about the rpm's that it gets, I picked it up as a project for my family to enjoy, and the 11p is what came on it. I tried to do a little research on the motor, and a few links that I came across say that an 11p prop should put me around 20mph at wot, and that for the merc 1150 motor, that prop would be best suited for a houseboat. I have a pic that the guy i bought it from sent me before i picked it up, so youll have a better idea of what i have.

 

[djrascoe]

Re: Prop pitch question

 

[Georgesalmon]

Re: Prop pitch question

Always bad to guess at a prop. Thinking if I had no choice but to guess I would be looking at somthing around 17ish. Thing is, no matter which prop you try you HAVE to know what the WOT rpm is to know if its the right one. Not kidding you HAVE to know.

 

[steelespike]

Re: Prop pitch question

As I understand it the inline 6 can be unforgiving if propped wrong and or timed wrong. Prop selection for any motor needs to be done with a tach and a gps for speed.Some cells have a gps app.
I agree a 17" is a good starting point.You may want to find a dealer that will let you try props with the understanding your going to buy.

 

[djrascoe]

Re: Prop pitch question

I dont wanna sound too dumb here, I'm really green when it comes to alot of things with boats, But does the tach hook up to the power head like it would on a car? I did notice the other day when I was out looking at the motor that there was a thicker black wire coming out of the motor, a little bit above where the lower unit bolts up, that has been cut. What would this wire be? I didnt know if it was a temp sensor, or possibly for the tack, or?? The dash does have a tach on it, I need to put the lower unit in a drum of water so I can fire it up again and see if it works. I haven't had the boat on the water yet, and when I did start it up, I was back looking around at the motor, and didnt even think to look at the tach and see if it worked or not.

 

[Georgesalmon]

Re: Prop pitch question

Is it really a wire? Or maybe the speedo hose? There is no temp sensor, put on by merc anyway. The tach sender on your motor is tan I think though it could be gray. It comes off of the stator and is connected at the rectifier and on to the remote control. On the front of your control there is a plug that has purple (ign), black (gnd) and tan sender (or gray). Those wires will power your tach. If the tach goes to 0 when you turn on the key it will likely work.

 

[djrascoe]

Re: Prop pitch question

Ill have to look at it again and see if its a wire or a hose. It may be a speedo, im not really sure what it is to be honest. I never thought about it being for the speedo, I have what I think is a sensor for the speedo on the transom, a few inches from the transducer, for the depth finder. But im sure that the one on the transom could have been an add on, and that may be why the wire/hose may have been cut and taped off. Ill post back on here when i get out to the barn to get a better look at it.

 

[steelespike]

Re: Prop pitch question

A gps is best for accurate speed information.Some cells have a gps app.

 

[djrascoe]

Re: Prop pitch question

So i had a chance to get out and look at the motor again today, and it is a hose, not a wire coming out of the motor just above where the lower unit bolts up. Im not quite sure what it is tho. It almost looks like it may run down to the lower unit and attatch somewhere by the water pump housing. Like I mentioned in an earlier post, it had been cut by the previous owner. Is this something that I need to repair, and where would the other end hook up to?

 

[82rude]

Re: Prop pitch question

post pics of the hose and the area,also post pic of dash ,its very hard to tell but doesnt that have a tac allready?maybe im just seeing things.i had a boat of similar weight with a 82 90 hp rude on it and used a 17p prop and was dead on for rpm,s id think you would be in the range of 17 or 19 p.personally i liked the 4 blade prop better than the 3 for my piglet.

 

[djrascoe]

Re: Prop pitch question

Ill try to get back out to the shed tomorrow, or monday to post a pic of the hose and area its in. It does have a tack, im just not sure if it works or not. I havent had the boat in the water yet, I just picked it up a couple months ago and im trying to get everything ready for this coming spring. I have only had the motor fired up for a brief moment just to hear it run, and when i did so, i was inspecting the power head and wasnt paying any attention to the dash. Ive been looking at aftermarket tachs just incase it doesnt work properly. Ive been looking at the 4 blade props also, but didnt know for sure what Id be better off running. This is actually my first real boat, other than a lil 12 footer that i had years ago. My main plans for this one are to mainly fish, and mabee pull the kids and wife around on a tube a few times or so. But after that Im looking into the nitro z series boats, or something in that neighborhood.

 

[djrascoe]

Re: Prop pitch question

Actually heres a pic of the dash that I just remembered I took, after I mounted my depth finder.

 

[dsay1]

Re: Prop pitch question

I'm green too when it comes to boats but I just bought a 17' boat with a 1978 1115 mercury on it. It has a 19 pitch on it. I took it out last week and it was hauling ***. I found a crack on the prop afterwards and just order a 17 pitch prop just to calm it down a bit.

 

[H20Rat]

Re: Prop pitch question

I'm green too when it comes to boats but I just bought a 17' boat with a 1978 1115 mercury on it. It has a 19 pitch on it. I took it out last week and it was hauling ***. I found a crack on the prop afterwards and just order a 17 pitch prop just to calm it down a bit.

What was your WOT rpm? Ordering a smaller prop could be a very bad thing for that motor.

 

[dsay1]

Re: Prop pitch question

Sorry I wasn't paying attention to the rpm at that moment, the waves were choppy and I was catching some air. Had to back off on the throttle, was getting a bit scary.

 

[V153]

Re: Prop pitch question

The hose coming from the gearcase connects to the speedometer. It's a built in pee-toe, if you will ...