F36 tri-cabin speed

[larryeddington]

All you Tri-cab owners with Crusader 270s, what RPM and what props are you using.

I can get about 3500 rpm tops and 21mph at WOT. My props are probably what came on it 20X17. Trying to figure what would get the RPMs in the power band 4200 to 4400?

BTW that was immediately after having the hull cleaned with hot pressure washer. So not hull Drag. Weight I guess it weighs 16000 according to the lift scale.

[prowlersfish]

No one ?

[P-Dogg]

It's a two-part question. I can't answer 'cuz I dunno what props are for sure......

Top end is like 4500 for me, for the few seconds that I dare do it. I usually cruise about 3000 to 3200 and get about 15 to 17 knots. And book sez my DRY weight is 18000. All from (a fading) memory.

[larryeddington]

Okay forget the book my boat weighs 16,000 with 60 gal of water and close to 200 gals of gas. The props are 3 blade 20X17 and I cannot get full RPM I know every 2 inches less of pitch is supposed to gain 400 RPM. Was just wondering what others look like in rpms vs speed.

Weight was obtained at haul out on lift, they have a gauge to calc weight.

[prowlersfish]

Book (the one I have) lists the tri as 1600 dry and travel lift scales are off a lot . With that said I believe you need to knock off some pitch Larry no mater what your boat weights . Assuming your tachs are right and engines running good . Use a prop calculator to find what you need . Adjust it to what results you have now to get good results . If I get a chance I will run them later

Are your props 20x17 for sure or is it what your think they are ? 3 or 4 blade ? gear ratio ?

[larryeddington]

the props are 20X17 3 blade for sure, read the numbers on hub myself. Engines are or seem to be running perfectly. I figure need less pitch or both less pitch and smaller prop. Has 270 crusaders which judging by the way they run are or would make the power at 4400 but cannot get there. Just put new plugs and personal rebuilt the Q-jets and clean bottom. Also I am reasonably sure the tachs are correct. Best speed via GPS that I have seen is 22 but doing that on less RPM.

Gear Ratio 1.91

[WayWeGo]

Props can be reworked to different pitch but not correctly marked. Are you sure about yours?

[larryeddington]

mine are originally stamped. But no not sure other than my other boat I have a set of props reduced by 2 inch of pitch which is the max either up or down. when I had them re pitched from 14X11 to 14X9 they xed out the original and re stamped it. The props on tri-cabin have only 20X17. I could have them reduced to 15 or use a smaller diameter prop. That is what I am trying to find out. I ordered a book on props. Wonder what speed at WOT other tri-cabs will run?

My F-28 still has 14X11 gonna try the 9s.'

[WayWeGo]

The props that came on my boat were resized and re-pitched by the previous owner. A year later, he had them re-pitched again back to the original pitch. The props were never marked with the changes, so going by the markings on the props would be misleading.

[larryeddington]

Way we go what dia and pitch is yours now.

[WayWeGo]

18.5" diameter, 19 pitch.

We usually can get to max RPM for our 440s with these props and a clean hull, but not always. Still need to install the Edelbrock 1409's and sort out some other stuff on the engines, but I suspect we will stick with these props. We usually cruise at 6-7 knots, so not a lot of performance data. Once I get the engines sorted and fuel flow sensors installed, I will do some testing and report the results.

[larryeddington]

I have purchased the book Propeller Handbook in hopes once read and understood I can make some definitive choices.

It so far has been very enlightening.

[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 ?

[Bob Giaier]

My 73 tri cabin has 400s. With 20x17 3 blade props. Don't recall the v drive and velvet drive ratios but it's all stock. I cruise always at 3000rpm and run at about 17-19 mph. I have had her up to around 3600rpm which was pretty maxed out at 24mph

I know this probably doesn't help but I did get a set of free 4 blade props of smaller diameter I think 16 x 17 . I need to check that. Anyways I put them on after nicking a prop back a few years ago when the lake levels were real low. The 4 blades are way smoother at any rpm. Unfortunately i couldn't go over 16mph. The boat had no load and would rev to any rpm , but man it was smooth. Anyways, I guess it's interesting to know if someone's getting better performance out of a diff prop set up.

[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.