Prop pitch specs

[Chopperbill]

I have a Suzuki 20 motor with a 10" pitch prop. My dad an ole boater from way back went for a ride with me and we had trouble planing. We are at 5200 altitude and lose HP here. He immediately said you need a prop. Went into his days what he did to get his to plane. Well for my birthday he bought me a 8" prop, which I'm thinking is just right. Is the RPM change the same on all boats regardless of HP? My motor max rated is 5300-6300 RPM. We just barely hit 5300 when we were out. Alone I plane ok and can just get 6000 at times.

 

[steelespike]

Smaller motors tend to react more to a prop change.In order to evaluate your setup we need the rpm and gps speed.
Your original rpm and gps speed lighty loaded as well.I think you lose a little over 15% at 5200'.
8" is about a 20% change. What size/type boat.Some small fishing boats are undersized and will struggle to plane weight.
What is actual size; length, width, transom width and height,setup,hp rating,aluminum,glass?2 or 4 stroke motor?
The antivent plate(just above the prop) should be about even with the bottom.
Try different trim settings.

 

[Sea Rider]

Check with Susy if they have High Altitude Jets, at that height you're losing about 25% of your current 20 HP. It's a combination of smaller jets and less pitch to overcome power loss to some extend while boating at elevations. Add engine well height seated on transom, trimmed and weight evenly distributed throughout deck and will plane faster with 2 or more up.

Incredible, you have passsed from a 9.8 to a 20 HP, and still with planing issues, very frustrating indeed. I'm begining to think that the SD 365 is under inflated or has strange behaviours..

Happy Boating

 

[Chopperbill]

Motor is fuel injected of course a 4 stroke. Jets not used. 9.8 with wife would not plane and do 8 mph. Suzuki 20 will plane with her aboard and do 20 mph. Problem shows when hauling a passenger at 70# more than her. Boats a 12' inflatable. Inflated at max pressure. High altitude kills these suckers. Boat is stored until we are at sea level in AZ. Just kinda want to know what to expect with the prop.

 

[steelespike]

Check with Susy if they have High Altitude Jets, at that height you're losing about 25% of your current 20 HP. It's a combination of smaller jets and less pitch to overcome power loss to some extend while boating at elevations. Add engine well height seated on transom, trimmed and weight evenly distributed throughout deck and will plane faster with 2 or more up.

Incredible, you have passsed from a 9.8 to a 20 HP, and still with planing issues, very frustrating indeed. I'm begining to think that the SD 365 is under inflated or has strange behaviours..

Happy Boating

AhHa an inflatable I missed that. Now I understand the struggles.

 

[Sea Rider]

Chopperbill,

Try your new less pitch prop and see what happens, definitely will achieve more rpm, how much, your current tach should tell you. If overrevving with you alone no issue when heavier 70 K mate is added, rpm will drop accordingly. Just for the record post your results. Fingers crossed, goog luck planning.

Happy Boating