Props

[Capt.Frank]

I am not a expert on wheels. I changed over to my spare wheels last year after haul out. Don't like them so getting others tuned. B31 3208 NA 210hp wheels 19 X 21 no cup. planned to just tune up and add a #1? cup does this sound right? boat runs 26-27knots Wot clean bottom 21-22 knots cruse @2400 rpms. with those props before. Only reason I ask is I thought most are running more of a square wheel 21X21. The wheels were out of spec a little but have not had them worked in 10 years or more I think.
Like everyone would like little more speed but am very happy with performance of boat. The guy at the prop shop say we could add more cup but I need to recheck WOT rpms on engines.

[scot]

Frank,

Will the strut length / hull clear a larger diameter prop? The larger the diameter, the more efficient (less slippage) the set up will be. 19" sound small for 600+ cu inches of CAT diesel. What gear ratio are you running?

Don't worry about the "over square" as my prop guru tells me that doesn't matter at all and is more of an old school train of thought. Run the largest diameter you can swing and pitch to match engine, if it's over square it doesn't matter. Keep in mind you need 10% of the wheel diameter clearance between the tip and the hull. (20" wheel needs 2" tip clearance, etc.) Also, some cup is almost always good.

[Capt.Frank]

Scott,
The struts are stock. Boat still in water, was trying to run boat and check rpms with photo tack but weather and family have been against that. I thought most guys are running 21" or 22" wheels.
What size wheels are other guys running?

[Bob H.]

Frank, I'm running 21" diameter cummins 350+hp.

[Tony Meola]

Frank

I have the 270 Cummins. I am running 20x23 with some cup. I turn up to 2650 at the top end. I know Uncle Vic ran 21 inch props with no problem.

[Capt.Frank]

OK, Thanks My plan is right now is to just tune these add cup. I have 3 other wheels may need to sell or trade for a pair of 21" for more surface area.
Help refresh my memory if in neutral the engine should turn to max rpm's? then when propped right engine should turn to max or close to max rpm's?

[Chum Bucket]

As I have been told by numerous Cat guys, at the dock (no load) you should turn AT LEAST your max rpms plus 100-200 more. I have a B33 with 3208T 320hp Cats with 23x21 cupped 4 blades. No load at the dock I turn 3000-3050. On the water with a light/med load, fuel tank full, flat water, I turn 2825-50 WOT which is perfect. Cat says my max rpms are 2800 WOT so I know I am not overloading the engine even with more weight. I'll run for hours at around 2200-2400, 22-24 knots. The last thing you want to do is over prop these motors for any length of time.

What's max RPM on the NA's? Buy a phototach (Harbor Freight) and verify your engines are actually turning what the tach says you are. Even my Aetnas were off considerably when I bought the boat.

[John F.]

Crows nest came with 2 sets of wheels. I'm trying the 4-blades this year, which I think are 20.5 x 20 with cup. DD 8.2s at 300 hp. Speed is pretty linear. 22 knts at 2200 really Rpms, 25 knts at 2500 Rpms, etc., up to 3150 to 3200 Rpms at 31 to 32 knts. She seems to run about the same loaded light or heavy, although she never really runs that heavy as I don't fish her offshore. I run her at 2200. Fast enough, and I need these things to last for awhile