prop pitch

[anchor man]

I have a Lund Fish. w/ 150 Yam F150. Started with the 21 pitch prop and topped out around 53mph at around 5600rpm lightly loaded. I tried a 19 pitch prop and gained rpms up to the 6000 mark, but lost about 2-3 mph. Is that normal to lose some top end? My motor is set at the lowest setting and the cav. plate looks to be even with the lowest part of the boat.

The only reason I tried the 19 pitch was to get the rpm on the higher end of the range since I was doing the experimenting lightly loaded. I figured with a couple others in the boat plus gear, the 21 pitch might bog down the rpm too much.

[marine_man]

Yes, going to a smaller pitch prop (going to 19 from a 21) you will lose some speed, but you will pick up hole shot. The 2 to 3 mph loss corresponds well with what I've observed in other situations.

In theory (in an ideal world, with no efficiencies or prop slip to consider) a 19 pitch prop would push the boat 19" in one revolution, where as a 21 pitch prop would push you 21" in one revolution, hence, the increase in speed.

You need to find the balance between speed and holeshot that you're most happy with. For me, while I like speed, I would prefer to have good holeshot when I'm fully loaded down or when pulling skiers or tubers... but that's me.

What you observed is the exact reason some people have a "power prop" (you're 19" prop) and a speed prop (21" prop). I prefer to have one prop and elminate the hassle of changing props to pick up 2-3 mph, which is minimal for most boat owners.

marine_man

[PierBridge]

I would find out what your safe RPM range is for your motor I would think 6000 would be about it.

You'll want that hole shot when you have a full boat with gear and gas.

[anchor man]

Pier Bridge,

The max range is 5000-6000 rpm for that motor. I have heard that you want to get as closer to 6k as possible. I'll probably stick with this prop and give up a couple mph. Either way you put it, 51mph is plenty quick for a walleye boat.

Thanks

[upnorth]

If you go with a stainless steel prop you wil probably get the lost MPH back. The aluminum flexes at high RPM and will lose a bit of MPH, stainless steel doesn't.

[marine_man]

An excellent point that I failed to make (Contact US Regarding This Word).. stainless would definately get you back your rpm while keeping your holeshot, or possibally improving upon it...

something to consider...

marine_man

[Tom Wilson]

AM,

I did a little checking and the Yamaha F150 is optimum at 5600 RPM that's why it came with the 21 inch prop. At 5600rpm that prop moves you at 117,600 inches per minute with the 21 prop. At 6000 rpm the 19 inch prop moves you at 114,000 inches per minute. If the prop you have is Aluminum, then a 21 in Stainless steel would roughly give you the same hole shot capabilities as the 19, and still maitain the top end speed of the 21. Again, according to the info that I found from one of the better testing resources that motor is optimum at 5600 rpm. It's a four stroke-think of it in terms of you car. Why would you run your car at 6000rpm's when you could get the same output from 5600 rpm's. Not to mention the fuel savings, and the wear and tear on the motor itself from the constant pushing of the upper level of the rpm limits. Two strokes and high output direct injection engines run differently, and are simply better when you push their upper limits. Not true with Four strokes. Bass and Walleye boat magazine does extensive testing of different motor/rig combinations and there lund and crestliner comparisons with the F150 each were at 53 MPH at 5600rpm's. You simply aren't gonna gain anything in the long run with the 19. The only way you could improve your situation would be to try a Stainless.

[marine_man]

Tom,

Which issue of B&WB was this information in?

Thanks!

marine_man