Prop. for 16'lund with F25 Yamaha 4 sroke???

[ravenhostel]

Hallo there,
I'm driving a 16'SSV Lund with a F25 short 4stroke I'm have the orignial
9 7/8x10 1/2 Prop. the RPM 5000-6000 r/min max. HP at 5500r/min.I have no
way of checking the actual Rpm with this prop.I'm looking to have a diveren't
Prop since I go most of the time with a light load (max two peopel)over long
distance (50 miles)or just fishing.The max speed with this Prop. is about 22 miles.I would like to increase the max. speed ,but not take to much away from
the mid range of speed.Could I go up to a 12pich or 13pich and what would I gane and what would be loose!Is the 9 7/8 the max. in diameter for my motor?
How about a four blade prop?Well,hope you can help me out!?

 

[Silvertip]

Re: Prop. for 16'lund with F25 Yamaha 4 sroke???

Diameter is not the key factor for any engine other than it must actually fit on the engine. Diameter is a function of design of the prop so you first find a listing of props for your engine. Pick the pitch and diameter will take care of itself. If you see two props from two different manufacturers but both with the same pitch, there is a fair chance they will be slightly different diameters and that difference is due to design. Since you have no idea what the current wide open throttle rpm is, it is impossible to tell you what will happen. In fact at this point, without that number you can't be sure you currently have the correct prop. Your question can be answered only generally. IF -- and only IF your engine indeed operates at or very near the upper end of the recommended wot rpm band, then increasing pitch will very likely slow you down, kill hole shot and cause the engine to work too hard (lugging) which will create problems down the road. Going the other way (less pitch) would help hole shot but again would cut down speed. IF - and only IF, the engine is reving too high, then an increase in pitch would be in order. There is no free lunch here. The engine must be able to twist a higher pitch prop to realize any benefit. If you have the correct prop now, top speed is what you have now. Adding pitch won't get you more because the engine can't twist that prop.

 

[steelespike]

Re: Prop. for 16'lund with F25 Yamaha 4 sroke???

Silvertip pretty much covered it.
You might borrow a shop tach or get a tinytach.Tinytach is reasonable,easy to install and will fit any similar motor without regard to stator poles.
There are some things you can do to be sure your getting the most out of your setup.Eliminate any extra weight distribute weight carefully.Raise the motor vertically 1/4" at a time by adding 1/4" sticks on top of the transom.
Raise to a point just before venting(cavitation) becomes a preoblem.
Carefully adjust trim.With your present rpm and speed careful prop selection may allow even more height and speed.

I did notice here at Iboats there was only one selection in a 10 1/2" pitch and a number of selections in the 11" pitch Including the turning point props. This may indicate the 11 is a typical selection.
Generally a 4 stroke is setup to run at or near it max rpm rating 6,000
in your case.From my limited research the turning point props generally provide overall improvement in most cases.Whether you can increase pitch depends on your present rpm.

 

[Wee Hooker]

Re: Prop. for 16'lund with F25 Yamaha 4 sroke???

FWIW, here's a link to the Mercury site where they test run a 30 hp 4 stroke on two different 16' Lunds using a 11" pitched prop. Not an "apples to apples" comparison but some interesting and usefull comparisons. Seems like you should be able to squeeze a few more MPH out of yours anyway.

http://www.mercurymarine.com/look_d...itle&Section=outboardChecks&fourStroke2530=10

BTW, Have you checked the engine/prop height?

 

[ravenhostel]

Re: Prop. for 16'lund with F25 Yamaha 4 sroke???

Thank's,so if I would assume my motors does 5800r/min.and I run a 10 1/2
what pitch would you use in order to increase top speed and be reasonably
sure that it would work overall!?
What is a turning point Prop!?
When you talk Engine/prop height is that raising of the motor at the transam!?

 

[steelespike]

Re: Prop. for 16'lund with F25 Yamaha 4 sroke???

Thank's,so if I would assume my motors does 5800r/min.and I run a 10 1/2
what pitch would you use in order to increase top speed and be reasonably
sure that it would work overall!?
What is a turning point Prop!?
When you talk Engine/prop height is that raising of the motor at the transam!?

First of all any prop change is an educated gamble."Turning Point" is a prop manufacturer their aluminum prop was the Hustler now apparently called Rascal.
These props provide close to stainless performance at Al. prices.Here at iboats about $60 plus the hub at $33.Once you have the hub you could change props at just the prop cost.I wouldn't change props without max rpm and speed info.Without you could end up with a motor that doesn't perform well or in the extreme suffers premature repair problems and possibly failure.
If I was doing it blind I would do the Turning Point Rascal in the same 10 1/2" pitch.
Yes; as described motor height is raising the motor on the transom.Do as described in my other post.Most motors can be raised an inch or so.Go a little at a time as described.The idea is to have as little as possible in the water and still pump water and perform right.Most new motors have provision for bolting when ideal height is attained.after you have the ideal setup you can decide if a new prop is necessary.The Rascal may allow even better height.
Simply raising the motor could gain a mile per hour or more with a slight improvement in mileage.

 

[ravenhostel]

Re: Prop. for 16'lund with F25 Yamaha 4 sroke???

I been looking for a prop with the same pitch and have found a Rascal
10 3/8 x11 the diameter is 4/8larger as my 97/8 is that still good to go!?

 

[steelespike]

Re: Prop. for 16'lund with F25 Yamaha 4 sroke???

If the prop is intended for your motor ;diameter is generally not part of the the consideration as long as it physically fits.Not knowing your present rpm going up in pitch is a bit of a worry.