Steve

I am sure you get about a hundred questions a day, but I was wanting your opinion. I have an 18ft Shallowsport with a DF140 Suzuki. 4 blade,17x23p fairly cupped prop that came with the boat. No Brand name, guy said that it was custom. It just seems that it lacks the hole shot with that much motor. (mabe because it is 4-stroke) I can get the over-rev light to come on at the top end. 42mph WOT. Does it sound like I am even close on correct propping? Thanks in advance...

Joey

Joey, not steve but here's what he'll say...

Four strokes are pigs for holeshot, it needs a lot of rpms to produce horsepower, if your current prop doesn't have adequate venting, allowing the motor to wind up and go, it'll always be slow.

You're in a catch 22 right now, poor holeshot, and not enough prop to keep it off the limiter. If you're looking to change (I would) then I'd be picking out a powertech flats four blade with large vents, that prop should give you the best all around results on your tunnel boat.

pretty much took the words right out of my mouth.

only question i have is, you said you have a 17X23p prop. You really have a 17" diameter prop on there??? if so that's the problem. you need to go down in diameter and up in pitch. And YES vent the barrell to allow the exhaust gas to flood the blades on the holeshot. ( 4 strokes need venting)

It's possible i can do a diameter reduction and increase the pitch on your current prop. And drill some vent holes.

Thanks for the help Pat and Steve. I did not even think about the venting. Steve I thought it was 17" I will go look and make sure. It could be a 13"x23p. I was not sure if a new prop or working on the old one would be the answer. Had it worked on at Nettels Prop shop in Austin last year and I asked about the venting but he said no. I will check on the prop diameter. Will the venting make a huge difference on the hole shot? Thanks again...

yes, venting that prop with a 4 stroke engine will make a huge difference.

since your over revving the engine, you'll also need to go up in pitch or have alot of trailing edge cup put into that prop.

LOL, I was thinking, man, if that engine can turn a 17 in diameter prop, he's got one hoss of an engine already!

i know, huh?? a 17" diameter prop would most likely hit the cavitation plate or trim tab.

Steve

it is a 13x23p. So can I just send it to you and are you thinking that venting and adding some more cup will do the trick?

yes, yes, and yes.

once i get it i'll be calling ya. so make sure you send me your phone number.

thanks.

23p on an 18ft ShallowSport, thats odd. Hell, I've been out of the saltwater scene for so long that it may not be. My Sport 18(1987 model) had a 140 Evinrude and I was running a 17p 4 blade Predator, it wouldn't over rev and jumped out of the hole.

Yeah 23 seems stiff, but every prop is different.

Most of the PT's I setup on tunnels were 15-17 pitch with V-6's, but everyone's unique.

What kind of gear ratio would the Suzy have? That has to be the difference.....I can't imagine a 140 pulling a 23 on an 18' boat with any kind of 1.7-1.8 gear ratio. Must be around 2.3:1.

Actually, I just did a few calculations using 42 mph and 10% slip. Figuring a 23" pitch and 6000 rpm, the gear ratio would have to be 2.83. I have the feeling that the prop is wrong for the boat, and has a very high slip rate.

Artie

i heard today that a suzy 4 stroke has a 2.95:1 gear ratio.

Well...that would certainly change things. And will certainly make finding the right wheel a challenge.