Propellers again

Mike_G · 08-12-2010, 10:15 PM

Hi Guys,

I was wondering if any of you could help me with finding (teoreticlly) what prop should I use.

Boat:
23 ft deep V twin step around 900 kg with engine and fuel (madness marine sr-23)
Engines, props, speeds, rpm so far:

MERC XR2 Racing, 24x14 3 blade E.T. 5900rpm 103km/h (1,87 CLE)
MERC XR2 Racing, 24x14 1/4 Chopper 5600rpm 98km/h (1,87 CLE)

Yamaha 200Pro V with modified heads (around 210 hp )
24x14 1/4 Chopper 6300rpm 109km/h (1.85 gear box )
25x15 Fury 5400rpm 104 km/h (1.85 gear box)
23x13 3/4 Laser II 6100rpm 106km/h (1,85 gear box)

I will repower my boat with Evinrude 250 H.O. with 1,71 gearbox, max rpm is 6000

What do you think? What prop should I start to test with? My biggest prop is 25x15 Fury but propably it will be too small

I prefer over hub props, I really love choppers. I was thinking about 26x14 or 28x14 but honestly I don't know if 28 would be to big.

Can someone help? Is there any way to calculate it ??

Mike

Mike_G · 08-12-2010, 10:23 PM

Most important...

I'm looking for good top end

So I don't think that 4 blade prop would be good idea

OCRDA · 08-12-2010, 10:33 PM

PM me your email address and i will send you a Excel file prop slip calculator !!

Bob

Mike_G · 08-12-2010, 10:35 PM

PM sent

Thanks

Burty · 08-12-2010, 10:49 PM

in my experience evinrudes need to run deep so you wont want a surface piercing prop. our 250HO on a heavy 21ft boat ran 78mph with a 25 trophy 4 blade and that was the fastest prop of about 10 we tried.

Mike_G · 09-12-2010, 08:41 AM

Quote:

Originally Posted by Burty

in my experience evinrudes need to run deep so you wont want a surface piercing prop. our 250HO on a heavy 21ft boat ran 78mph with a 25 trophy 4 blade and that was the fastest prop of about 10 we tried.

4 blade... what kind of boat it was?

Burty · 09-12-2010, 06:19 PM

700xs, the new Gav design, I believe the cyclones also run 4 bladers on there 250HO's

Mike_G · 09-12-2010, 08:08 PM

Hard to believe that 4 blader is faster than 3 blader

in quite light hulls

I'm saying light couse it is not 23ft US Bowrider

What about Fury or Tempest ? Any experience with that props?

Burty · 09-12-2010, 09:16 PM

no mate, we tried, lasers, rakers, et lightening, choppers, trophies and a bravo 1.
maybe its the gearcase design??? i know someone that went from a 280 to a 250HO and he had to drop the motor 3" to get the same sort of bowlift and performance

Mike_G · 10-12-2010, 07:23 AM

allrhight mate
So I will start with 25trophy :-)

Cheers

Burty · 10-12-2010, 07:26 AM

none of these boats were stepped though, maybe try sending Adam a pm as he ran a 250HO on a 23ft stepped hull

Mike_G · 10-12-2010, 07:28 AM

that is also good idea

thanks

grandmas denture · 10-12-2010, 08:16 AM

Quote:

Originally Posted by Mike_G

MERC XR2 Racing, 24x14 3 blade E.T. 5900rpm 103km/h (1,87 CLE)
MERC XR2 Racing, 24x14 1/4 Chopper 5600rpm 98km/h (1,87 CLE)

... which engine height ?
... fueltank at bow or back ?
... xr2 must rev 7000+ for max hp

Mike_G · 10-12-2010, 08:43 AM

prop shaft is about 1,5 inch below bottom line
fuel tank at back of the boat

Never seen over 6400 rpm even on my old ring 20C even after rebuilding the engine

Paul Howes · 10-12-2010, 08:54 AM

This might help

We have been testing Adam Younger 24ft Batboat with 250xs. Various engine heights and various boat weights due to our class restrictions. Results are as follows.......

Lowest engine height (boat 950kg)

Bravo 1 28 5400 76.5 mph
ET Lightning 28 5700 79.6mph
Tempest 27 5900 82 mph

Height plus 1 inch (950kg)

High 5 25 6200 72mph
Tempest 27 6000 83mph
Bravo 1 28 5600 78mph

Height plus 3 inch (950kg)

Tempest 27 6500 87.7mph

Height plus 1 inch (1050kg)

Bravo 1 26 6100 78mph
Tempest 27 6000 82mph

Great speed from high engine setting but real lousy handling, turning not recommended.

We have decided best race set up is Tempest 27 at plus 1 inch for flat race and Bravo 26 for rough race. Boat handles much better with 4 blades rather than 3. adding 100kg of lead at pivot point in keel makes the boat handle like a dream.

Hope this helps

Cheers Paul

Mike_G · 10-12-2010, 08:59 AM

So basicly Tempest was the fastest one.
But it is 250XS so propably sport master
and 250H.O. will not run over 6000 rpm

Still thanks for help

Any advice apprciated

Scand · 28-01-2011, 06:47 AM

Quote:

Originally Posted by Paul Howes

This might help

We have been testing Adam Younger 24ft Batboat with 250xs. Various engine heights and various boat weights due to our class restrictions. Results are as follows.......

Lowest engine height (boat 950kg)

Bravo 1 28 5400 76.5 mph
ET Lightning 28 5700 79.6mph
Tempest 27 5900 82 mph

Height plus 1 inch (950kg)

High 5 25 6200 72mph
Tempest 27 6000 83mph
Bravo 1 28 5600 78mph

Height plus 3 inch (950kg)

Tempest 27 6500 87.7mph

Height plus 1 inch (1050kg)

Bravo 1 26 6100 78mph
Tempest 27 6000 82mph

Great speed from high engine setting but real lousy handling, turning not recommended.

We have decided best race set up is Tempest 27 at plus 1 inch for flat race and Bravo 26 for rough race. Boat handles much better with 4 blades rather than 3. adding 100kg of lead at pivot point in keel makes the boat handle like a dream.

Hope this helps

Cheers Paul

What was the hight of the propeller shaft in relation to the keel at the lowest setting?