Which pitch prop to move to?

[wasilvers]

I have an older aluminum "v" style boat (1978 sea nymph) - current prop is a 3 blade, 12'', 13pitch prop designed for pontoon boats. It moves the boat at exactly 25mph and the motor hits the rev limiter real quick. The boat jumps right on plan but at wide open throttle the engine seems to have so much more to give, just not enough prop there. So the question is, do I move to a 15, 17, 19 pitch or ???

Boat details are:

• Boat weight per nada = 600 lbs center console
• motor is a 50 hp evinrude with a 2.4:1 gear ratio - weight 200 lbs est
• 1 battery, 1 livewell , 6 gallon gas tank, 1 trolling motor
• boat plate says the max motor size 55 hp, I have a 50 hp 2 cycle motor
• carrying capacity is 800lbs ?

Please help me if you have any ideas or what you are running.

Thanks for any help,

Will

 

[solar7647]

Re: Which pitch prop to move to?

Well the first peice of info you need is what the recomended WOT RPM should be for your engine. The manufacture recomends a power curve that can be found in the engines repair book, online or some times is on the engine it self on a name plate. It will be a range an example of this is it would say "4400-4600". Now rule is that the lower the pitch the higher the RPM the higher the pitch the lower the RPM. The pitch is the estimated distance in inches that the boat will move in one rotation of the prop, so your speed will decrease or increase with your change this will very though because it does not calculate for slip or loose of bit due to cavatation that all props have. So for example if you recomended RPM is 4500rpm at WOT but you are only hitting 4200 RPM you would decrease your prop pith by 1 inch this should have a 200-300 RPM change increaseing it to 4500. It would be the other way if you were over by 200-300 RPM you would increase the pitch by 1 inch. Now I use a four blade composit prop that you can adjust the pitch through a range of 7 inches startes at 15 ends at 21. This works great and is very handy because it allows you to adjust the pitch according to the conditions, large loads, small loads, rough water, smooth water, fishing to tubing it realy gives you control of how the boat handles. Its made by pro-pulse you may want to take a look if you change activities alot. They do cost more so if you are just fishing or cruising you may want to stick to a 3 blade alum prop.

FYI. When ever you post a questions about your engine or prop always include the make, modle year and Recomended WOT RPM and HP. You will find it faster in getting the answer you need.

 

[solar7647]

Re: Which pitch prop to move to?

Oh forgot one thing, the more you increase your pitch the more it may take to get on plain. This is because a higher pitch will loose bite faster then a lower pitch.

 

[wasilvers]

Re: Which pitch prop to move to?

Engine recommended rpm range is 4500 - 5500.

Engine is a 1989 Evinrude 50 hp VRO motor with the 'small' gearcase. Current prop is # 775713 12.5" x 13" Prop - by Hydrus(?)

I'm not certain on the wot rpms. My tach reads at 5100, but I'm not sure that is correct. The rev limiter engages when I'm at full throttle and cuts spark (thus rpm sending pulses) till it gets back down. I'll have to find a way to check the tach and maybe change the pole setting.

For right now, getting on plane is no problem. I even loaded my wife and 3 kids in the boat and it went right up. I had a 250 lb fisheman and put him in right in the front of the boat and she still went right up. Almost threw him in the back of the boat. From WOT, I can pull the throttle down, then work the trim till rpms go right back up and then the rev limiter kicks in again. I'd like to go to a 17 pitch, but it seems like a big jump from 13 and I'd hate to ruin the holeshot - but 25 mph seems so slow....

I'll look into the composite prop you mentioned below- any idea who makes it?

Thanks!

Will

 

[yellowbelly]

Re: Which pitch prop to move to?

those pro pulse props are no good the one i bought for my 55hp rude lasted 60days the back of the hub split in half when i was cruising one day

 

[captkevin]

Re: Which pitch prop to move to?

Think I'd go up one size & try a 15 pitch. See how that does & go from there. Might check out ebay for your prop - have found some great deals.

 

[hwsiii]

Re: Which pitch prop to move to?

Silvers, the perfect prop for you will be a 16" Pitch, it will run your boat at about 33 MPH at top of the RPM range of 5,500 RPM. Be forewarned, you will lose that head snapping hole shot, but you will be gaining about 33% in speed to makeup for it. My program shows you actually need a 17" prop but I feel the 16" will be a compromise with speed and hole shot without raising your RPM too high for your setup. If you can't find a 16" go with 17" as the 15" will still be a problem with over revving too much with that gear ratio of 2.42:1.

H

 

[wasilvers]

Re: Which pitch prop to move to?

Silvers, the perfect prop for you will be a 16" Pitch, it will run your boat at about 33 MPH at top of the RPM range of 5,500 RPM. Be forewarned, you will lose that head snapping hole shot, but you will be gaining about 33% in speed to makeup for it. My program shows you actually need a 17" prop but I feel the 16" will be a compromise with speed and hole shot without raising your RPM too high for your setup. If you can't find a 16" go with 17" as the 15" will still be a problem with over revving too much with that gear ratio of 2.42:1.

H

Thanks a million! I'll be ordering via iboats soon!

Will

 

[junior1113]

Re: Which pitch prop to move to?

agree 17 not 15 let us know what happens