finding the right prop

[GodsReel]

thanks guys, i guess i think i will try a 4 blade when i have the cash, i would like to have a slower plane speed for certain days , got caught in ches. bay coming back from drum fishing in a stacked up 4-5 ft NE 20-25 and needed a slower plane speed . thanks for all the help.

[shine]

Originally Posted by GodsReel

thanks guys, i guess i think i will try a 4 blade when i have the cash, i would like to have a slower plane speed for certain days , got caught in ches. bay coming back from drum fishing in a stacked up 4-5 ft NE 20-25 and needed a slower plane speed . thanks for all the help.

or a bigger boat

I had a chance to run the new 17 pitch 15.25" 3 blade in the river (pretty flat water) and there is still cavitation unless the motor trimmed almost all the way down.

I was getting some good numbers though: One tank of fuel (55 gallons), three adults and a child on board, I ran 27 mph at 3900-4000 29/30mph at 4200-4300. Hooking up the fuel flow this week so we will see where the best fuel burn comes in at.

I believe the next step will be to lower the motor a notch

[Fr. Frank]

Pay close attention to the mounting height of your motor, If you're still ventilating (It is NOT "cavitating") at any motor trim angle other than pretty well trimmed down, I would suspect one of three causes:

1: motor mounted too high (this would also explain slow time to plane with accompanying cavitation upon hard acceleration from a standstill)
2. insufficient cupping on the trailing edge of the propeller blades OR full cupping not extending to the middle of the blade tips
3. A wake obstruction on the hull ahead of the propeller/lower unit such as a through-hull fitting or transducer.

Cavitation is air bubbles forming on the trailing side of the propeller that is caused by pressure differential, and results in reduced "bite" and reduced thrust.

Ventilation is air bubbles being pulled down from the water's surface to the trailing edge of the propeller. The whole purpose of cupping a propeller is to minimize ventilation, and yet still allow a propeller to run right at the water's surface, minimizing drag and friction.

[eggsuckindog]

Since it is at all trim angles your choice would be to lower the engine 1 hole or look for a prop that has more rake - basically longer sweeping blades

look at this pic and pay attention to the blade design
http://www.boatownersworld.com/Props...age_series.htm

my previous prop acted the same as yours, could not trim at all without it blowing out, although no cavatation except trying to trim it. It was a standard Merc prop similar to a Vengence - rounded blades kinda like mickey mouse ears

The Stilletto I have now is another hole higher and I can't get it blow out at all - careful on RPM, a prop like that will knock off 200/300 RPM per same size

On another note - when looking at them recently they are priced at $250 new which I thought very reasonable with prices I have seen

[bumpdraft]

I had a 15x15 prop on two different Johnson engines(235 and 200hp) before getting a 225 Yamaha 2 stroke for my 23. I put on a 14"x 19" prop and it made it feel like a different boat. It was fine for flat seas, but I didn't like the ride when it got rough. I eventually got a 15 1/4x 17 Saltwater series and was very happy with the prop. I changed to a Yamaha 225 four stroke with that same prop and I was only able to get 5400 rpm. I have since changed to a Solas 14 1/2 x 15 four blade and can get 6100 rpm. I should probably have a 17 " pitch, but it will do for now. I'm saving my Saltwater series, hoping to get a 250 four stroke.

[shine]

lowered my motor 2 notches, it is now about 4" above bottom of keel. Very solid bite

Fuel flow shows 9-9.5 gph at 30 mph and 4200 rpm (into stiff wind), a little better with the wind (light load, 2 adaults, 2 tiny kids and 55 gal fuel, no ice, empty boat well)

27 mph at 8.5gph, 3900, into same wind.

I did not try any slower, but I dont think it get much better, we will see.

Im happy

[eggsuckindog]

Suggestion - its really hard trying figure 3 different boats in one thread - just say'in