Composite Props

Chris Martin · 03 January 2005, 21:10

Firstly , as a new member, may I say hello to forum members. Over the Holiday period I have spent several hours looking at current and past threads finding a lot of them to be of interest and also some quite amusing.
A bit of advice though, or perhaps the benefit of others experience. After destroying an aluminium prop to about 10% of it's normal blade length and just managing to creep back to terra firma, I needed a replacement quickly to continue my holiday boating fun. A like for like replacement was not available 'off the shelf' and I pondered for some time before purchasing a composite, adjustable pitch prop. I viewed it as a temporary use prop, though the vendor assured me that lots of people now use them permanently. I must admit the performance seemed no different, maybe even better. I'm now unsure whether to go back to an ally prop and keep this one as a spare, or continue with the composite. On first thoughts the idea of a plastic prop didn't seem right, but then lots of products made today are plastic rather than metal. Another thought is whether the replaceable composite blades would shear off flush and leave less chance of getting back to base. I know it would be sensible to carry spare blades, but then you've still got to fix 'em in a possibly dodgy situation. I am hoping I will learn the pros and cons through this forum, to enable me to arrive at a more calculated decision.

Thanks,
Chris Martin

codprawn · 04 January 2005, 00:36

Thanks for the info Chris - have lthought about these myself - it is mainly the variable pitch that interests me - though wether or not suitable for 225hp don't know!

As to composites being suitable as you said loads of things going down that road now - including helicopter rotor blades and plane props.

Paul F · 04 January 2005, 00:52

you must be running a different prop as the normal one supplied with engine as that one is a very popular size and carried by most dealers.

As for non metal ones, would be nice to know what hp they will take and what sort of price difference to bog standard alloy ones.
Paul

Richard B · 04 January 2005, 00:54

Hi Chris,

Interesting to hear your experience with the composite prop. I must warn you that you are now the RIBnet composite prop expert - I hope that is not too daunting a prospect after your first post!

We have carried a spare composite prop since we've had the current boat, but never used it - perhaps after your positive comments we'll give it a go, although we do carry a spare stainless steel prop anyway.

Codders/Paul F - our Piranha is supposed to be suitable for up to 260hp (their website now says up to 280hp). See www.piranha.com But if you're interested in a variable pitch, you should ask jwalker about his Torqueshift which sounds very impressive - he may still have it for sale!

Welcome, Chris!

codprawn · 04 January 2005, 02:51

Quote:

Originally Posted by Richard B

We have carried a spare composite prop since we've had the current boat, but never used it - perhaps after your positive comments we'll give it a go, although we do carry a spare stainless steel prop anyway.

Codders/Paul F - our Piranha is supposed to be suitable for up to 260hp (their website now says up to 280hp). See www.piranha.com But if you're interested in a variable pitch, you should ask jwalker about his Torqueshift which sounds very impressive - he may still have it for sale!

Welcome, Chris!

You actually HAVE one and haven't used it!!!! Come on - just not good enough - we need ALL the details we can get!!!!

Richard B · 04 January 2005, 06:19

Sorry! I'm not sure if it's got the correct hub splines for our motor!

mstacey · 04 January 2005, 10:13

I've been using a variable pitch composite four blade prop fitted to my Suzuki Df140 18 thru 22 pitch is available manually adjustable and can be done with the prop still fitted on the engine.

Carry the Ali prop as a spare

See http://www.propulse.se/ for the one I am using

Swifty · 04 January 2005, 10:17

Regarding plastic props...
I also do alot of boating with Kent Scouts. We operate off a shingle beach that has a lot of shallow bits with lots of different helms and some are more careful than others...
We were getting through a few props in a year so decided to try the Piranha range. Performance was virtually unchanged, although we were only running on a 30hp yam 2str and not too intersted in flat out speed. We chucked a spanner and a few spare blades into the safety box and waited with baited breath.
When you wrap a rope it would seem to survive ok, but I would guess most rope wraps are at low rpm. But come into a hard sand or shingle beach, even at tick over and twang there goes another blade. They would shear off at the narrowest part, which is right down at the hub, and would not leave anything to get you home. I dont remember ever seeing all 3 blades gone, but I suppose it would be easy to trash 3 blades.
The cost of blades against a new prop is gonna be a long debate, but it seem to boil down too how often do you ever touch bottom- the hard type! An ally prop will suffer from a grounding but would normally get you home, and can generally tolerate much more abuse. A plastic prop gives up alot easier.
After a season we went back to ally props. It seems to work better for us for where we are and what we do.
Last year I ran aground once in my own boat. I was a safety boat for a large Scout event where we had 100 kids afloat, when a squall blew through. We initiated an 'all in' rescue and everyone was recovered quickly. We were in about 2-3 metres of water before the squall but a 1 metre chop meant we started clipping the bottom. Every single boat dinged a prop to some extent. In this case had I a plastic prop I would have been severlly hampered or even disabled. As it was all I did was bend two blades, one through the middle of the cup! This was easily straightened out as it wasnt chewed.

So if you have a soft bottom and dont touch it, the plastic option may work for you.

Searider · 04 January 2005, 10:37

Quote:

Originally Posted by Richard B

Sorry! I'm not sure if it's got the correct hub splines for our motor!

Not a great deal of point in carrying it then

Chris Martin · 04 January 2005, 19:20

Sorry, my post might have been slightly misread. I was not offering advice or experience, as Richard B may have thought, regarding composite props but rather asking for any advice or thoughts on these props. Hence let's make it clear that I am no expert on the subject!
Sounds like 'Swifty' might have confirmed my suspicions that on impact you can lose too much of the composite prop to be able to limp home.
Although I think the prop on my engine is pretty common in size, it was not easy to find a stockist in the Pembroke area of Wales. Maybe others had already obliterated their props and beaten me to the parts counters in the area.
Perhaps the answer is to carry an ally prop as well. Just in case.

Chris Martin

jwalker · 05 January 2005, 00:04

I did a fair bit of testing using the Piranha prop a few years ago. Number one, the first one I got had an incorrect distance from the bronze insert containing the thrust taper to the front of the hub. It appeared ok after fitting but it was so close that once the propshaft endfloat was taken up by the thrust, it rubbed against the retaining ring inside the gear casing. Using the lathe to remove a few though off the front edge fixed it. Also, the machining of the taper in the bronze was not circular... back to the lathe. The guys at Piranha were very helpful and pleased to know about it and a later hub was ok. But, nevertheless, it's an indication of the quality control at that time. I can't comment on it's impact strength. I don't hit things with my gear casing.

The performance was pretty good on a 200hp merc. It had good acceleration and it gripped pretty well. When it finally broke loose, it easily recovered and regained its grip. It reduced the top end speed by about 3-4mph and, despite trying various pitch blades, I could not regain the speed. This is in comparison with a merc ally prop with teddy bear ears for blades.

I changed to a torqueshift which was initially disappointing but when I really learned how to set it up properly and how to drive it, I never looked back. I tried other stainless props but nothing came close to the handling and grip in all conditions and the softening of the ride in bumpy conditions.

Richard B · 05 January 2005, 00:26

JW - what setup is required for the Torqueshift? And have you still got yours for sale?

jwalker · 05 January 2005, 00:39

I had two, sold one and I'm keeping the other for when I feel the need for speed again and buy a Phantom.

Setting up is done to match the boat and the way you wish to drive it. There is a range of cams which control the rate of pitch change. There are also springs which modify this rate to fine tune the setting. There are maximum pitch adjustment screws too but, when you get it right, these can be set to maximum and the setup controls the maximum pitch. When it's right, it's cool. However, you can do a reasonable job by setting the maximum pitch using the screws and benefitting from the progressive pitch change only. Provided the cam selection is in the right ball park.

roohairy · 06 January 2005, 07:24

Jwalker,

This torqueshift sounds like a good idea, never heard of it before. Do you know how much pitch change it will give, what is the variation in pitch?

Thanks,

quinquarimarine · 06 January 2005, 09:00

For about 7 years we used plastic props on our commercial operations on twin instalations with up to pairs of 175s powering 10m boats with 12 pax.

The pyrana prop is probably the better lived though not as well engineered as the propulse. The propulse has the advantage of being adjustable but the blades do tend to sheer off after a while when simply under load ( to be fair our loads can be extreme). With both you are limited on sizes if running a counter rotation as well. We also set our cavitaion plates quite low (about 20mm below intersect) and open up CL of engines which no doubt helped a twin instal. using plastic props.

There was probably about 10% loss in general efficiency. Cavitation is slightly higher with a full load as would be expected.

We still carry them as spares but do now fit all of our boats with 3 or 4 blade s/s props as for marketing reasons it is "required" of us. There is a potential issue on warranty of gearbox if not using a dedicated prop.

No doubt the better the prop the better the performance but at the same time the plastic probs do seem to come up with good results and overall cost is about 30% of s/s whilst on damage and assuming just one blade broken then cost of replacement is about 10% of s/s.

As an aside it is possible that the plastic prop is more ecco when considering impact with cetaceans and pinipeds at low speed. Whilst still causing lacerations they will not be a severe as a ss prop.

Cheers

John
www.quinquari.co.uk

codprawn · 06 January 2005, 12:24

Quote:

Originally Posted by jwalker

I had two, sold one and I'm keeping the other for when I feel the need for speed again and buy a Phantom.

Setting up is done to match the boat and the way you wish to drive it. There is a range of cams which control the rate of pitch change. There are also springs which modify this rate to fine tune the setting. There are maximum pitch adjustment screws too but, when you get it right, these can be set to maximum and the setup controls the maximum pitch. When it's right, it's cool. However, you can do a reasonable job by setting the maximum pitch using the screws and benefitting from the progressive pitch change only. Provided the cam selection is in the right ball park.

Having seen the video on their website the acceleration looks awesome - so much so it worries me a little bit - if you are going fast and leap out of the water does the change in pitch happen so fast that you might get such a surge of acceleration that you flip the boat on landing???

Simon B · 06 January 2005, 13:36

We ran a Pirahna prop on our lead dive boat a while back, the logic was that we had a number of new boathandlers and if they ran into something the prop would break and save the gearbox.

The first time this happened the fact that it couldnt limp home on the what would have been bent remains of the ally prop spelt its death knell, this despite the fact that the same mob had to borrow my socket set to get the old one off, not having anything onboard to change the prop with. As a method of quick change and repair they are good, we didnt notice any loss in efficiency but youd have to be super sensitive to tell on a dive RIB full to the gunnels.

Obviously the doomsayers did not reflect upon its gearcase saving potential. I can post some pictures of the snapped blade. We carry one now as spare and run ally as a main prop.

New blade set = £25-00
Steel dev repair = £36-00 (ish)

If you are in the habit of having only the one prop and wont or cant change the prop at sea then stay with ally. If there is the chance of gearcase damage you'll get a lot of blade sets for one gearcase.

jwalker · 06 January 2005, 14:07

Quote:

Originally Posted by roohairy

This torqueshift sounds like a good idea, never heard of it before. Do you know how much pitch change it will give, what is the variation in pitch?
Thanks,

Yep. There are two alternative blade sets available, one is 11" - 26" and the other is 14" - 32".

Quote:

Originally Posted by codprawn

Having seen the video on their website the acceleration looks awesome - so much so it worries me a little bit - if you are going fast and leap out of the water does the change in pitch happen so fast that you might get such a surge of acceleration that you flip the boat on landing???

Nah. If you are running fast then the prop will already be pitched up. It will pitch up on a jump but it just comes back down as you land. You will be unable to tell it is happening. Your notion is correct though. On landing you have good power as the prop re-enters the water. Just what you need.

Don't let the vid fool you. If you watch the porpoising and look at the engine you can see that there is more trim than you would want for a good start. It's probably done for dramatic effect... it's worked on you...

Back to the plastic props.... The Piranha, compared to a S/S prop, is VERY light. This must be good for the dogclutch in the gearbox.

Simon B · 06 January 2005, 19:59

Here are the broken blade shots from an encounter with an orange fishing float (hard GRP? type) you can just see a smudge of GRP and some melted blue polyprop rope on the edge of one of them.

They are quite strong given the are a composite the float was drawn into the prop and managed to bend the AV plate into a gentle curve before the blades failed. Again not sure how ally or SS would have faired

quinquarimarine · 07 January 2005, 01:01

Quote:

Originally Posted by jwalker

Back to the plastic props.... The Piranha, compared to a S/S prop, is VERY light. This must be good for the dogclutch in the gearbox.

Nope ... JW you seem to have a good idea of engineering but I must disagree on this one. Forgive the words but a positive dog if what you want rather than a slack one.

Cheers

John
www.quinquari.co.uk