folding prop - no reverse??

[Dipper]

for restricted budget reasons I was going to get one of those Radice 2 blade folders - but if theyre not to efficient in forward gear i'm so sure now (not so bothered about reverse to be honest

I can maintain 5 knots on a calm/slight sea with a 9HP Volvo and a 26ft boat. I have motored all the way from Weymouth to Dartmouth without any problems. Usually if there are any waves there is also wind so I sail. Under sail is when the folding propeller really comes into its own.

 

[Tranona]

Some points:-
.

Generally most marine gearboxes give about half the forward shaft rpm in reverse.

So you'll probably need x2 the rpm to get a similar thrust.

Not sure that is true. The Yanmar KM boxes have either 3.06 or 3.16 in reverse and the smallest reduction in forward is 2.2 but in yachts the more common forward ratios are 2.6 or 3 to 1. TMC boxes are 2.3 reverse and 2.6 forward and Volvo similar.

You are right, however that if there is a big differential then reverse performance will be even worse. One solution is that with some feathering propellers like the Featherstream you can have different pitch settings for forward and reverse.

 

[contessaman]

My gearbox is a watermota 'J' type. Looking at the exploded diagrams it does not appear to use cones, but a large number of flat metal discs acting as a large clutch. every other disc is on the output shaft and the gear lever just slides the whole thing in or out of contact with the discs that are being rotated by the engine. The whole thing sits half submerged in standard engine oil and the manual warns of damage occuring if it were filled with heavier gear oil. The manual does specifiy some adjustment for reverse and also mentions a reverse brake band but the whole process looks to be rather like a black art unless one has done it before so I may just whip the box out over winter and send it off. After all, its been at least a few weeks since I last shed several hundred pounds in the name of boat ownership and the money is burning a hole in my pocket. Perhaps I should stand outside in the rain and rip it up....

p.s. twister ken. Did you ever race against 'riot'??

 

[snowleopard]

A lot depends on the blade design. A heavy blade will force its way out against the flow of water much better than a lightweight job.
With mine (2-blade flex-o-fold), putting the engines into full astern will stop the boat in its own length from 11 knots.

 

[Twister_Ken]

"Did you ever race against 'riot'??"

Rings a bell, but the only other OOD34s I can actually remember the names of were Bruce Bank's 'Windsprite' and a Cloggie called 'Twee Gezusters'. The RAF had one with a big roundel on the kite - maybe called 'Red Arrow?' I think my 'owner' had the OOD for three seasons, so I had three years racing (and cruising) it. Way back when they were new boats.