F36 tri-cabin speed

[larryeddington]

I have the same 20x17 but 270 crusaders so with less power the best speed ever was 22 mph I think with a tail wind and rpms maxed at 3500. I agree with paul, I am sure I will need less pitch and or less diameter.

I am really wanting to know what speeds our tri-cabs get at WOT and 4400 pms.

Once I finish this book I may know a reasonable answer to achieving it.

[prowlersfish]

Unless you both have the same engines and gears any comparing is useless . Big difference between a 440 turning 4000 and a 350 turning 4400 Waywego your boat calls for 20x21 or 20x20 are you sure of the prop size ?

Pretty sure -- I have the Prop Scan sheets from Black dog on them.

Seem small but if they where 4 blade w/some cup I could see it

[WayWeGo]

Unless you both have the same engines and gears any comparing is useless . Big difference between a 440 turning 4000 and a 350 turning 4400 Waywego your boat calls for 20x21 or 20x20 are you sure of the prop size ?

Pretty sure -- I have the Prop Scan sheets from Black dog on them.

Seem small but if they where 4 blade w/some cup I could see it

3-blade with no cup, which seems strange to me as well. The engines are not over-revving at full throttle and everything else seems to be OK.

Maybe the boat is heavy with too much junk aboard? Have never had it on a travel lift to see what their scale says.

[larryeddington]

Way we go, What speed does she go at WOT and 4k rpm?

[WayWeGo]

I never paid that much attention, but about 24-25 mph by gps, as best I recall. Once the fuel flow sensors go in, I am going to test and record data...

[larryeddington]

thanks, Mine is way too slow.

[WayWeGo]

thanks, Mine is way too slow.

I agree with prowlersfish that your situation is quite different from ours. Your boat has a greater displacement and smaller engines, making direct comparisons difficult.

Maybe some of the folks with tri-cabins can be of more help...

[prowlersfish]

I have the same 20x17 but 270 crusaders so with less power the best speed ever was 22 mph I think with a tail wind and rpms maxed at 3500. I agree with paul, I am sure I will need less pitch and or less diameter.

I am really wanting to know what speeds our tri-cabs get at WOT and 4400 pms.

Once I finish this book I may know a reasonable answer to achieving it.

Larry are your gears 2 to 1 ?

[larryeddington]

Paul I think they are 1.91 to one but will check next time at lake, it is on the tranny tag

[prowlersfish]

Larry , running some numbers a few inches less pitch is called for . But I would think about going 1" , reason being is as you go up in rpm the engine will be able you pull harder and give you even more rpm . Like to se a HP graph

[larryeddington]

I am going to do the calcs per this book which according it can be pretty accurate. I agree less pitch for sure, however these props are spendy so cannot just try one after the other. The bigger diameter the proper the more efficient if you have not over pitched it. I am pretty sure when it is said and done it will be 15 or even 14. But not presupposing. Will run the calcs at weight, draft, L of water line and width at water line and HP at 4400 RPM.

Understand I am not trying to make this waterborne boat a speedboat but trying to get her max when desired.

Which I had 671s but not going to happen.

[prowlersfish]

I am going to do the calcs per this book which according it can be pretty accurate. I agree less pitch for sure, however these props are spendy so cannot just try one after the other. The bigger diameter the proper the more efficient if you have not over pitched it. I am pretty sure when it is said and done it will be 15 or even 14. But not presupposing. Will run the calcs at weight, draft, L of water line and width at water line and HP at 4400 RPM.

Understand I am not trying to make this waterborne boat a speedboat but trying to get her max when desired.

Which I had 671s but not going to happen.

I would re-pitch what you have now . Remember the results are only as good as what you put it .

[larryeddington]

Can only go up or down 2 inches pitch. See what the cslc says.

[prowlersfish]

Unless you both have the same engines and gears any comparing is useless . Big difference between a 440 turning 4000 and a 350 turning 4400 Waywego your boat calls for 20x21 or 20x20 are you sure of the prop size ?

Pretty sure -- I have the Prop Scan sheets from Black dog on them.

If you want to go with 4 blades Mitch just sold his F36 and is selling his spare set https://minneapolis.craigslist.org/dak/ ... 29869.html

[larryeddington]

Paul I do not think the 4 blades would help as they are 20x19 if I take 2 inches pitch out I am at 20x17 with 4 blades. Me thinks would be worse than now.