Honda BF50D prop question

[blecina]

Hi,

I use Honda BF50D with shallow V (12 degree) aluminum skiff. The boat is 16ft/6,5ft and engine is connected via NMEA2000 to my MFD. Boat weights ~ 1050lb all hardware installed (engine, battery, gas tank, MFD, seats, anchor). Prop is 3x11.25x13. I'm getting 32mph@6150 alone (240lb) with fishing gear (40lb) , 31MPH@5900 with three adults and gear ~700lb.

I'm interested in top speed. I usually go up the river and drift downstream fishing. I consider moving to 3x11x15. I wonder if that change makes sense. How do you think?

Thanks for any help.

 

[Sea Rider]

Welcome to Iboats,

Will need to answer yourself if "always will be boating as described" What's the min-max wot rpm range for that 50 HP ? A 15 pitch will lessen wot revs while increases top speed, how much ? can't possibly tell, need to test that prop on combo going up river. Is river up flow exact same year round, varies with rain, whatever ?

Happy Boating

 

[blecina]

We usually fish in two, three is occasionally. The min-max RPM range is 5500-6000, peak output @5750.

The WOT rpms are:

- down river 6200, up river 6100, av. 6150 alone
- down river 6000, up river 5800, av. 5900 in three.

Speeds provided in first post are also average (33,70 down, 30,1 up, 32,5down, 29,4 up)

This is large river with stable flow for most of the year. The flow will be rather less from current value. I don't run WOT during the flood - my buddy had really bad experience. He hit flowing submerged tree trunk during flood @WOT.

I will keep current prop for heavy load situations. I just wonder how will RPM's change when I drop dia slightly and add 2" of pitch. I know the rule of thumb is 200 per inch of pitch and 300 per inch of dia, but I also have heard it's not always like that with small pitch props.

 

[Sea Rider]

If wanting revving near 5750 wot revs as loaded, might go 1 pitch up to a 14, if not available could re pitch current 13 prop to a 14 in a prop shop. A 15 will drop too much rpm down, will increase top end speed a bit, but hole shot will decrease. On those described boating conditions personally would prefer better hole shot.

Rule of thumb has never worked right for my light applications when maximizing props, one less pitch achieved 300 to 500 + wot rpm. Know going for a 0.5 pitch increase for OB to rev at it's max wot range factory stated.

When playing with props need to test them as usually loaded, a prop investment is mandatory and from there fine tune pitch to suit your boating needs.

Happy Boating

 

[ahicks]

15" sounds like a good plan from where I'm sitting. You're over revving under some circumstances now, and you have no plans to pull anything, so I'd go for it. Worst case, you can have one of the props repitched a little for a 13" vs. 15" compromise.

 

[blecina]

My feedback after some testing:

I changed to 15 and got 5550 upstram @30MPH in two, and 35 @5750 downstream. I haven't tested alone yet, I suppose I will gain 2-3MPH . I noticed slightly worse hole shot (as suspected). However, the fuel consumption @WOT dropped slightly (17L/h vs 18l/h). I think the best prop for my boat and this engine would be 14 pitch. Thank's all for feedback. Next season I'm starting witch new BF60, so I will swap prop when I get my boat for storage and I think it should be fine with new engine.