Penta Duoprop

[BruceK]

Has anybody swapped between B4 and B5 props?

Not interested in WOT etc but am very interested in rev difference. So for example, did you see a rev difference at 20knts of 100, 200, 300 or 400 rpm etc.

Single or twin engine installation?

thanks in advance

Bruce

 

[Scarron]

Yes I have; just checked my prop testing logs

25 ft deep vee, very heavy at 3000kgs
Single V8 petrol 290 DPD1 Drive 1.78 ratio.

B4
20knots@2,750
25knots@3,250
30knots@3,750
41knots@5,400

B5
20knots@2,600
25knots@3,050
30knots@3,400
35knots@4,000
43knots@5,000

I ended up using C4 props as the best compromise which gave more revs and speed. Now on a DPX-A drive with E series props and more power

Every boat and rig is different but I hope that is useful context.

 

[vas]

is that on a sonny levi hull scarron or a fairey?

 

[Seastoke]

I use the MBc4 props

 

[BruceK]

Yes I have; just checked my prop testing logs

25 ft deep vee, very heavy at 3000kgs
Single V8 petrol 290 DPD1 Drive 1.78 ratio.

B4
20knots@2,750
25knots@3,250
30knots@3,750
41knots@5,400

B5
20knots@2,600
25knots@3,050
30knots@3,400
35knots@4,000
43knots@5,000

I ended up using C4 props as the best compromise which gave more revs and speed. Now on a DPX-A drive with E series props and more power

Every boat and rig is different but I hope that is useful context.

That's superb info thanks. Interestingly at max throttle and speed I noticed a 400 rpm difference between C3 and C4 as well so that matches the B4 B5 difference and B5 gave me ~200 rpm less than the C4 which tallies with what you are saying.

 

[Scarron]

is that on a sonny levi hull scarron or a fairey?

She's a Levi hull, with 25 degrees of deadrise, so deeper than the Faireys and heavier.

Back in 1968 GRP was heavily laid up especially when built to meet Lloyds A1.

 

[Scarron]

That's superb info thanks. Interestingly at max throttle and speed I noticed a 400 rpm difference between C3 and C4 as well so that matches the B4 B5 difference and B5 gave me ~200 rpm less than the C4 which tallies with what you are saying.

I would say the 30 knot comparison is the best benchmark, properly on the plane and at 3,750 rpm around peak torque. By 5,400 rpm it's passing peak power and coming off the top of the cam.