Prop for staying on plane at low speed

[NascarNHIS]

Prop for staying on plane at low speed

Boat = 1989 Sea Nymph SS175 FISH & SKI Aluminum (same as Starcraft SS)
Base weight 800lbs dry, beam 6’10” length 17ft.
Normal load = 800 lbs. (2 fat guys, lg cooler of beer and food 3 batteries, 2 tackle boxes, 2 small anchors, trolling motor, 15 gallons of gas safety gear etc.)
Deep Vee, bow rider, do not know degrees of deadrise
1989 EVINRUDE 48SPL 48 hp
Mfg. 4500-5500 RPM WOT range
2.42:1 gear ratio
Existing prop = 11 ? x 17 pitch unknown manufacture – fairly worn with a just a few small dings.
Normal use - Cruising as SLOW as I can and stay on plane, fishing with trolling motor

My memory might be off a bit but I think I max out at 21 mph @ 5200 rpm wot.

My goal is to stay on plane at lower speeds. I do not mind losing some top end. I run a lot in a river with a 10 mph speed limit and can only stay on plane around 13 mph

My guess is I should go to a four blade prop. Of unknown size and pitch

Michigan? Sola? Quicksilver? Hustler?

I want to stay with aluminum, please DO NOT recommend a SS prop.


thanks in advance.

 

[jestor68]

Re: Prop for staying on plane at low speed

Your prop is OK, according to your WOT rpm. A Doel Fin will get you on plane and hold you on plane at a slower speed(about 10 mph).

If you want to use a 4 blade, go one inch less pitch than your 3 blade prop. Solas props are hard to beat.

But, frankly; your solution is the $40 Doel Fin. Goes on in a few minutes.

 

[tpenfield]

Re: Prop for staying on plane at low speed

Are you running a 3-blade aluminum? you could go to 4-blade and down a bit in pitch.

 

[steelespike]

Re: Prop for staying on plane at low speed

I can't think of any boat like yours that will plane normally at 10 mph.
Minimum planing speed is usually around 13 mph.
If you manage to force it to plane at 10 you will be wasting fuel.
If you run at 6 mph your mileage would be around 12 mpg if you push it to around 7 the mpg will drop to about6 or 7.
The best practical planing speed is usually within just on plane and about 1000 rpm higher and is around 9 mpg.
Typically the higher end around 4000 produces better mileage. after planing.
If you insist on 10 mph trim the motor down put more weight in the bow so it won't try to climb over the bow wave.
4 blade props are said to have stern lift at low speeds and bow lift at higher speeds.

 

[cr2k]

Re: Prop for staying on plane at low speed

Planing a boat is the property of hull design/speed and NOT anything to engine or prop.
A fin on the back will help to some extent.

 

[NascarNHIS]

Re: Prop for staying on plane at low speed

Thank you all for your comments. I get it. I was just hoping to try and put out a smaller wake in this speed restricted area. At 10 mph I make quite a mess. I'll just add a Dole Fin and travel at 14mph and hope for the best. Thanks again.