Help with prop pitch?

[Robbo76]

Hi all,

I was wondering what would be the best prop pitch for my old haines v17c. I bought the boat 4 months ago off my uncle, it has a 135 merc opti on the back. Out at sea it seems to go pretty good once flat out, but at idle to half throttle it kinda bogs for a second then gets up on plane. It sits on 32 knots flat out, 6000-6500 revs, not that I do this all day, but does this sound right? I only have 3 people max on the boat with esky and all gear, mostly just 2 people and gear. I'm just after a good pitch I should use for good bottom to mid and for better fuel consumption, not to worried about going light speed. Oh, and on the prop it says 23P. I have 2 props he gave me, the s/s 3 blade on now and a 4 blade s/s.

I don't know if this is affected by prop pitch, but when trolling, every now and then the opti starts beeping and goes into "limp mode" for a few seconds until I stop and start again, overheating I guess?

Any suggestions would be appreciated. Sorry if it sounds all over the place, my wife is talking to me and i'm trying to pretend to listen and type at the same time. Who says men can't multi-task .

Cheers,
Rob

[Duckfish]

On a 17C, I would have thought a 19p prop would be the go as I had one on a 17L with a Mariner 135hp. The 17C and 17L are the same underneath. I suggest that you take the 23p off and try a good 19P prop. Something is not adding up right. With a 23P you are pulling top revs but the speed is down. The engine going into "limp mode" is not good. Mine was doing that and the problem was the two throttle postioning sensors were faulty. You best get it looked at professionally.

Duck

[Robbo76]

Will look into a 19, thanks. With the "limp mode" it only starts beeping about 1 in 4 trolls. When speed picked up it goes away. I was told it has 3 senses, and the top always reads a different temp to the bottom, sounding the alarm and not to worry bout it? Will get it checked out anyway.

Rob

[Robbo76]

I have found the 4 blade stainless prop in the shed, it's a 17p. Is this any good?

Thanks,
Rob

[wrxhoon]

Robo,

23" pitch prop and revining 6500 or even 6000 rpm you should be doing at lest 60 mph , sothing doesn't add up here .

Your opti should have a rev range of 5000-5600 and a cut-out at high 5's.

If you had smartcarft it would tell you what the problem is when she goes on lipm mode.

[oldboot]

If you buy the genuine manual specific to that motor....it should have prop tables in the front with part numbers.
The manual will also tell you recommended WAT range....and also where the motor rev limits.

remember pitch is only half the equasion.......you need to know pitch and diameter.....

Is the tacho set correctly.........if it is a 4 cylinder motor with the tacho set to 3....that will read high......most mercs WOT out arround 4.5 to 5.5....some motors have a narrower recommended WAT range....

If it is a merc tacho... the manual will show how it should be set too.

cheers

[Robbo76]

Hi oldboot, It's a v6 135 saltwater 01 model. Now that you mentioned it, I think the tacho starts at 1000. No manual with motor, also it is a merc tacho. I will give it a run on tuesday in the inlet and test it again, maybe the gps speed reading is off? it sure seems fast to me. I will also try the 17p 4 blade and see how that goes, I'm guessing the 4 blade would be a lot slower, but more bite.

Thanks,
Rob

[oldboot]

Go to a merc dealer and get a manual while you can....probaly cost arround $80.

cheers

[gofishin]

...remember pitch is only half the equasion.......you need to know pitch and diameter.....

Rob, this is a very important statement.

If the diameter is not written on the side of the prop hub, you will need to look at boss on the fwd most side of the prop (i.e. closest to the front of the boat). Some people call this the back of the prop - just to confuse things . There will be two numbers, written as 'diameter x pitch'.

Also, as others have said, something doesn't add up with those figures, especially WOT. Is it 6000 or 6500? It can't be both, and even 6000 is too high for your donk. A quick i-search revealed 5000-5600 Rec WOT range (1999 boatpoint test).
cheers

[Robbo76]

Hi gofishin, The tacho starts at 1000, and flat out i can get it to 6500. So really your right, 5500 flat out minus the 1000. Thanks for the info about the prop, will look into it today.

All the best,
Rob

[wrxhoon]

Robbo,

A boat the size and weight you have and a 135 Opti ( these are big motors at 2.5lt and they use the same engine to make 175 hp), you should use a 21" pitch or a 19" if its very heavy when loaded .
Sure the diameter makes a difference but its the pich that indicates what speed the boat will travel at certain RPM . You can work this out by dividing the given RPM by the final drive ( in your case 2.00-1) then multiply that by the props pitch , that will give you the speed per minute in inches . You will have to allow for some slip as well in your case around the 10%.
Thats why I said something doesn't add up when you said 6000 rpm with 23" pitch and you are only doing 32 kn.

At 6000 rpm and 23" prop you would be doing: 3000x23"=69000" per minute 69000x.0254= 1.7526 mts per minute X 60=105.156 kmh less say 10%=94.64 kmh =59 mph . I was right on the ball when I said you would be doing 60mph.

You have a decent size motor there for the boat and with a 21" pitch if you could get say 5500 at WOT you will be doing about 50mph , with a 19" about 45 mph .

I have little doubt that you will have a 5600 WOT with a 19" but I don't think you will get that with the 21" but you should be well within range .
Personaly I like to be on the upper end of the range ( very close to max with normal to light load) but as long as you are in range you are well proped .

Anything smaller than 19" it will be to small in my opinion and a 23 maybe a little on the big side .

I would have to tacho checked if I was you to make sure it works and if you have a GPS check the speed at WOT with the GPS . Using the calcs I gave you, you can work out the RPM at a given speed as long as the prop you have is stocker you will be very close.

[Robbo76]

wrxhoon, thank you for your input, much appreciated!

It does carry a bit of load. I have an 80 litre fuel tank under floor(center)and 60 litre up front between the bunk seats. Throw a home made large glass esky and a coulpe of 90kg blokes she gets a bit heavy. Also the donk is 210kg!

I think the tacho is off, looked at it this morning and it's sitting on 2000 rpm? I'm sure it was sitting on 1000. Stuffed if I know. The 17P S/S 4 blade I got I might just sell then. Will try again on tuesday and see how it runs.

Thanks again,
Rob