Need Help on Propping a Sea Voyager 42

[Old Duke]

I am re-propping this year and have some questions. My current props are 4RH21 and 4LH21, 1 1/2" shaft, 3-blade props on a 42ft., Trojan Sea Voyager, 1968, weighing in at 35,000 lbs. Engines are 68', 427 Ford Interceptors at 300 hp.

With that, can someone tell me what the "4" and "21" in the numbers 4RH21 and 4LH21 mean, how do I find the pitch and know if the current props have been cupped. I am currently looking at the Michigan Wheel 4-blade, 21" brass props for replacement. Is it true that I can get better fuel efficiency and smoother cruises with the 4-blade over the 3's?

Any help would be great.

Thanks

[rossjo]

4xH21 is ?" dia x 21" pitch - not sure what 4 is - Michigan Wheels?

Recommended prop from: http://www.BOATDIESEL.com Prop Calulator = 18x20.5 cupped 3-blade with 2.5:1 - not sure what your trannys are.

Suggests 4.4:1 w/ 29x28 3-blade.

I assumed 2.5:1 transmissions and an 18" dia prop:
MAX PERFORMANCE
Available Power: 582.0 SAE hp ( 434.0 kW) @ 4500 RPM
Max Speed: 17.4 kts
Fuel: 35 US Gall/Hr (typical)
CRUISING PERFORMANCE
Cruising Power: 119 SAE hp ( 88.8 kW) @ 2500 RPM
Cruising Speed: 7.9 kts
Fuel: 7 US Gall/Hr (typical)
RECOMMENDED PROPELLER
Diameter: 21.8 in. Pitch: 15.9 in.
Blades: 3 Cupped: No
Increasing the transmission ratio will improve prop efficiency.
PROPELLER BASED ON INPUT DIAMETER
Diameter: 18.0
Pitch: 20.5
Blades: 3
ALTERNATIVE GEAR/PROP COMBINATIONS
Gear Ratio Shaft RPM Dia. Pitch
2.4 1875 20 15
2.6 1731 21 17
2.8 1607 22 18
3 1500 23 19
3.2 1406 24 20
3.4 1324 25 22
3.6 1250 26 23
3.8 1184 27 24
4 1125 28 25
best#1> 4.2 1071 28 27
best#2> 4.4 1023 29 28
best#3>4.6 978 30 29
4.8 937 31 31
5 900 32 32
5.2 865 32 33
5.4 833 33 34
5.6 804 34 36
5.8 776 34 37

[Old Duke]

On the phone this morning with General Propellar out of Florida. Looks like the coding 4RH21 is a 21" Dia, RH rotation prop and pitch not in the number. Talking with GP, they are recommending running a 23" Dia. X 20" pitch using 4-blade for cruise.

rossjo: You are rigth on the Parigon (Velvet Drive) Tranny's 2.57:1 ratio. I could not get into your prop calculator site to run these numbers from GP. I was just curiouse to see if the recommendation came up with different numbers on the 4-blade, but you have to be a member to use the tool.

Currently looking at the Michigan Wheel, Bronze, 4-blade, 23" Dia. X 20" Pitch prop. Would like additional imput on this before I make the move.

Looking for some places to start looking for good prices or possibly used props. Already have information from GP and Propellers on Line.

[rossjo]

$25/year for http://www.BOATDIESEL.com - invaluable!

Anyway - the 23x20' will never work ... you'd need a 3.4:1 gear ratio to turn that!

23" 4-blade cupped @ 2.57:1 is a 23x1.6 -

recommended prop is 20.9 x 15.2 ...

best combination (gears and props) for a 4-blade is 4:1 26x24

http://www.BOATDIESEL.com__________________________________________
MAX PERFORMANCE
Available Power: 582.0 SAE hp ( 434.0 kW) @ 4500 RPM
Max Speed: 17.4 kts
Fuel: 35 US Gall/Hr (typical)
RECOMMENDED PROPELLER
Diameter: 20.9 in. Pitch: 15.2 in.
Blades: 4 Cupped: Yes
Increasing the transmission ratio will improve prop efficiency.
PROPELLER BASED ON INPUT DIAMETER
Diameter: 23.0
Pitch: 12.6
Blades: 4