folding prop - no reverse??

contessaman

contessaman

Well-Known Member
Joined
29 Oct 2009
Messages
823
Visit site
My OOD 34 has a 30 hp seapanther diesel with a 2:1 j-type gearbox swinging a 17x10 2 bladed folding prop.

Forward thrust is acceptable for a racing yacht- around 4-5 knots cruise at 60-70% rpm
Reverse is a different matter. I'm not expecting much with the folding prop but If theres anything of a wind blowing me into the pontoon berth I cant even reverse out against it.
As an experiment, with the engine in forward gear at just 1000 rpm, I cant really hold the boat from moving forward with all my strength on the mooring rope. In reverse I can pull the boat forward against full power with only one hand.

My fathers little 1/4 tonner has an air cooled 7 hp ducati diesel and a tiny 2 bladed folder. Its not exactly quick in reverse but its more than adequate.
Why is mine so poor?!

I can see the prop open and turning under the water. But no thrust!

Any ideas or similar problems out there??
 
Folding Prop

I think you may have the wrong prop. An OOD 34 with a 30hp engine should be able to motor at around 6kts. at 3/4 engine speed.
I have a 33 ft boat, a bit lighter, but with a 3 blade folder on a 29hp engine. At 2,000 revs. in flattish water I get 6.2 kts, with a sea and headwind we only need to increase to 2,250 to maintain this speed. When we are giving the engine its regular full power workout or against the tide at 3,200 we can exceed 8 kts. however fuel consumption then goes from 2l./hr to 7 l./hr. Even our old Sigma 33 would manage 6kts.
Astern we can stop from 4 kts. in a boat length. The three blade is exceptional but does have a bulkier profile when folded, but you should definitely be doing better with a good 2 blade.
 
Quandary said:
Astern we can stop from 4 kts. in a boat length. The three blade is exceptional but does have a bulkier profile when folded, but you should definitely be doing better with a good 2 blade.
Click to expand...

Hmm. With a 29hp Volvo, a two blade folder and a 7 tonne boat, I can achieve 6kn at 75% revs in a calm so the prop must be about the right size, but as far as reversing is concerned it's poor. The prop is functioning OK but from 2 knots there is no way I could stop in a boat length or even 2 lengths. The prop is a Radice.

P.S. Would have expected an OOD34 with a clean bottom and a 30 hp engine to do more like 6 kn at 70% revs.
 
Last edited:
Folding Prop

My 3 blade folding prop is a Volvo and I have been amazed by the power transfer it gives us.
However it is very expensive and I thought long and hard before specifying it, it also need a set of anodes every year at about £30. However having always had two blade folders in the past I don't regret the expenditure, particularly as we are berthed on a canal and are in and out of tight locks sometimes in very windy conditions. I believe the OP should be able to cruise at 6kts with a 2 blade folder except in adverse conditions if the boat is propped right, his expectation of 4-5 kts. is slow even for a racer. When we raced a Sigma 33 we usually could motor home from Tarbert to Belfast Lough in 13-14 hrs. and it had a much smaller engine, this allowed some of us to get to work the next day.
 
wotayottie said:
The prop is functioning OK but from 2 knots there is no way I could stop in a boat length or even 2 lengths. The prop is a Radice
Click to expand...

I have a Radice prop on a Volvo saildrive and a 9HP engine. It can stop my 26ft boat in it's own length from 4 knots but most of the 'action' is in the last 10ft.

They have quite heavy blades compared with some so I'm surprised you are having a problem but there obviously must be a reason for it.
 
thanks for all the responses people.

In general answer to a few points that have been raised;

I bought a book called the propeller hanbook, full of tables and graphs. If I am reading them correctly 17x10 is about right for my engine and gear ratio.

The prop is definatly not jamming as I can lay down on the pontoon and look at it spinning underwater with the engine in reverse gear.
The blades look to be almost completly open - not quite as much as in forward but I guess in reverse its a balance between centrifugal force and the thrust on the blades.

I was wondering if my gearbox could be slipping? maybe I need to try a handheld tacho on the shaft?

The hull is clean and I agree that I should be getting more speed from a sleek hulled yacht with a relativley powerful motor.

Twister_ken - im guessing that the OOD you raced had the original seapanther? Im 99.9% sure my engine and prop are as supplied by jeremy rogers, so I must be looking at a technical problem rather than a mis-matched prop for eg.? was that 'Red Otter' BTW?
 
Don't think this is prop related - I think you're right about your gearbox slipping in reverse. Had a similar issue with an old yanmar.

The checks you spec would be right.

Nudge
 
Dipper said:
I have a Radice prop on a Volvo saildrive and a 9HP engine. It can stop my 26ft boat in it's own length from 4 knots but most of the 'action' is in the last 10ft.

They have quite heavy blades compared with some so I'm surprised you are having a problem but there obviously must be a reason for it.
Click to expand...

I thought mine stopped in the same sort of distance but I proved it didnt by rogering the pontoon a couple of weeks ago.

I believe it's typical - the prop is free to open fully (checked 2 weeks ago), the clutch isnt slipping, and the prop is the correct size. I reckon its just an issue of needing to rev fairly high to get the blades to open fully.
 
To drift the thread a little ...

I have the Radice folding prop on a 20hp saildrive (30 foot boat). I had thought of replacing it with the Kiwi prop. Is it worth the money? Would I see any difference under sail and when motoring?
 
wotayottie said:
I thought mine stopped in the same sort of distance but I proved it didnt by rogering the pontoon a couple of weeks ago.

I believe it's typical - the prop is free to open fully (checked 2 weeks ago), the clutch isnt slipping, and the prop is the correct size. I reckon its just an issue of needing to rev fairly high to get the blades to open fully.
Click to expand...

Agree. I have a Radice 2 blade folding prop and it needs a lot more welly in reverse. It's not a terribly efficient prop, I can get up to about 5.5 kn in flat water but any sea to speak of and she slows right down. It does however give a bit of an advantage when under sail.
 
huzar30 said:
To drift the thread a little ...

I have the Radice folding prop on a 20hp saildrive (30 foot boat). I had thought of replacing it with the Kiwi prop. Is it worth the money? Would I see any difference under sail and when motoring?
Click to expand...

Can't see any advantage under sail and probably a disadvantage - the Radice does fold to a pretty low drag shape. Cant comment on the effect under power, but I cannot imagine anything but an improvement in reverse.
 
KenMcCulloch said:
Agree. I have a Radice 2 blade folding prop and it needs a lot more welly in reverse. It's not a terribly efficient prop, I can get up to about 5.5 kn in flat water but any sea to speak of and she slows right down. It does however give a bit of an advantage when under sail.
Click to expand...

I have one as well and it's the same.
 
we had a similar problem with our folding prop. Then one day I lost forward drive as well. It turned out to be the silicon liner which stops the shock of the blades opening being transferred to our sail drive.

We had to replace our prop completely.

Cheers
Rob & Annette
S/V Blue Lady
 
Some points:-

You don't specify the type of gearbox (ie is it cone-clutch engaged), but if it is it may be a simple matter of adjusting the lever to increase the travel. Cone clutches rely upon the rotation between the mating faces to lock, if the travel is insufficient the shaft will appear to engage, but not transmit any torque.
You can test this by putting into reverse and finding out if the shaft is locked (use a lever on the coupling as even if not fully engaged it will appear locked to the hand). I'd suspect this as the most likely cause of your problem - I had it on forward gear with a Yanmar box, did strip it between tides on Castletownbere beach; found the selector forks had worn on one side; reversed them and solved the problem.
A less likely cause is that the cones (due to previous slipping and overheating) have become lacquered by burnt oil. The only cure for this is stripping the box and regrinding the cones using grinding paste.

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.

Folding props are notoriously poor in reverse gear as centrifugal force is reduced by thrust-effort.

Perhaps an experiment - use full revs in reverse to open the prop fully and then reduce.
I certainly have to do this with my Autoprop, mainly because it takes about 2 shaft revs to reverse the pitch of the blades.

Otherwise I fear it's something you have to live with, a weakness of 2-bladed Radice folders.
 
Last edited:
wotayottie said:
I thought mine stopped in the same sort of distance but I proved it didnt by rogering the pontoon a couple of weeks ago.

I believe it's typical - the prop is free to open fully (checked 2 weeks ago), the clutch isnt slipping, and the prop is the correct size. I reckon its just an issue of needing to rev fairly high to get the blades to open fully.
Click to expand...

I do need to give it full revs to stop in a boat's length and at slower speeds I also need a burst of higher revs for it to be effective. :eek:

Others have commented that folding propellers are poor in reverse compared with fixed blades. This is not the complete story. Folding propellers don't perform well when the engine is in reverse but the boat is still going forwards as the water flow tends to encourage the blades to stay closed. If the boat is going backwards with the engine in reverse, the water flow actually forces the blades open so there is much less of a problem.

On the subject of forward speed in a sea state, I have the same loss of performance as the others. This is only really a problem if the wind has dropped but the sea is still lumpy or if I want to motor directly into rough seas on a windy day.
 
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
 
You must log in or register to reply here.

Share this page

Top