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Old 17 January 2010, 03:23   #1
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Fantastic plastic or not ???

When I bought my rib it had 2 x 50 hp Handa engines fitted.

In fact it still does but the props are plastic made by a company in the U.S.

They have a hub and 3 x removable blades.
To alter the pitch you just change the blades.

any good or should I now be looking to get alloy or a steel prop.?
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Old 17 January 2010, 04:30   #2
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I've seen them advertised but I wouldn't fancy the idea myself! No scientific basis just the idea of detachable blades puts me off.
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Old 17 January 2010, 05:01   #3
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Quote:
Originally Posted by BogMonster View Post
I've seen them advertised but I wouldn't fancy the idea myself! No scientific basis just the idea of detachable blades puts me off.
Stephen - I would have thought that was a selling point. If you dint a blade at the moment you need to take the whole prop off and send it away for repair. (In your part of the world that is expensive and slow - so you'll need 2 props) Damage a resin prop and you slide out the damaged blade(s) slide in a spare and off you go. Want to try a new prop pitch just order the replacement blades - significantly cheaper (and lighter/smaller to post) than a whole new prop. Given your limited second hand market for the old prop and low chance of borrowing props to try - it seems a good idea for far flung places!

Now back to the OP's question: I assume they are these? http://www.piranha.com/ they are not hugely popular but I don't think there is any real reason for this other than that they are not supplied as OEM and are a bit different so people are wary. Maybe your are loosing a tiny bit of top speed or acceleration or both - but if that was critical you probably wouldn't have picked a twin engine set up like that. In the back of my mind I think Nos4r2 said he had used them and was fairly positive about them. Are your engines a counter rotating pair? Can you use the same replacable blades in each (that would save having 2 spare props - if you carry spares). Personally if its not broken (i.e. they are doing what you want) then why fix it...
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Old 17 January 2010, 05:11   #4
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Those props are a great idea in theory, but in reality can be a pain. If you catch a piece of rope or touch the bottom in shallow water then they have a tendancy to loose all of the blades, whereas if you had an ally one then all you do is bend a blade or two but you can still get home again. If youre not going to be going in shallow water, then id go for stainless. IMO best allround for performance/reliability is to stick with alluminium props.
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Old 17 January 2010, 05:57   #5
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On the 2 occasions I dinged (dung...?) a prop it was quite a big ding, so just ordered a replacement having read mixed comments about sending them away to be repaired. Got two old ones under the bench now, might take them north next time I am away and try out the refurb route.

My concern is shedding blades as described, what happens if you hit a big kelp bog (occupational hazard around here), would plastic blades survive that or not? You can get home in an emergency with a bent blade and low speed, but getting home with a blade or two missing is going to be a non starter.

How does the efficiency compare - if I understand it correctly you use stainless because the blades are thinner and stiffer, so does a plastic prop end up having to be thicker than an alli one so it is strong enough?

Cost for only changing one blade certainly compares well with a new alli prop!
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Old 17 January 2010, 06:14   #6
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blades for prop

Quote:
Originally Posted by BogMonster View Post
On the 2 occasions I dinged (dung...?) a prop it was quite a big ding, so just ordered a replacement having read mixed comments about sending them away to be repaired. Got two old ones under the bench now, might take them north next time I am away and try out the refurb route.

My concern is shedding blades as described, what happens if you hit a big kelp bog (occupational hazard around here), would plastic blades survive that or not? You can get home in an emergency with a bent blade and low speed, but getting home with a blade or two missing is going to be a non starter.

How does the efficiency compare - if I understand it correctly you use stainless because the blades are thinner and stiffer, so does a plastic prop end up having to be thicker than an alli one so it is strong enough?

Cost for only changing one blade certainly compares well with a new alli prop!
I have had the rib for a long while now and so far they have not hit the bottom.

I carry a few spare blades with a lot of other kit and have again not had to change them.

The prop blades are there just in case along with a spare prop nut.
I have no problem with them except the fact there Plastic.

I have a few spare at home as well if they ever get damaged there just go in the trash .
approx 15.00 each.
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Old 17 January 2010, 06:19   #7
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a counter rotating pair?

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Originally Posted by Polwart View Post
Stephen - I would have thought that was a selling point. If you dint a blade at the moment you need to take the whole prop off and send it away for repair. (In your part of the world that is expensive and slow - so you'll need 2 props) Damage a resin prop and you slide out the damaged blade(s) slide in a spare and off you go. Want to try a new prop pitch just order the replacement blades - significantly cheaper (and lighter/smaller to post) than a whole new prop. Given your limited second hand market for the old prop and low chance of borrowing props to try - it seems a good idea for far flung places!

Now back to the OP's question: I assume they are these? http://www.piranha.com/ they are not hugely popular but I don't think there is any real reason for this other than that they are not supplied as OEM and are a bit different so people are wary. Maybe your are loosing a tiny bit of top speed or acceleration or both - but if that was critical you probably wouldn't have picked a twin engine set up like that. In the back of my mind I think Nos4r2 said he had used them and was fairly positive about them. Are your engines a counter rotating pair? Can you use the same replacable blades in each (that would save having 2 spare props - if you carry spares). Personally if its not broken (i.e. they are doing what you want) then why fix it...

Both engines turn the same way so just a couple of spare prop blades on the boat should do both engines.

But if both engines ever hit the bottom I guess with all the prop blades on both engines and the spares would make one prop to get me back home.

Yes there piranha props.

Maybe a little thicker than ally props. but if I wanted to change the pitch I just have to order blades.
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Old 17 January 2010, 06:26   #8
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My experience of them is that they are fairly good props. They hold the water well, they are light so load the gearbox less, especially when selecting gears also the blades can be cleaned up very easily if a little damaged. The down side for me was a lack of efficiency, the boat was noticeably slower at maximum speed. I guess this also equates to higher fuel consumption. Whether it's worth paying for two replacement props for a change, well, I doubt it. If they work well for you, stick with them.
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Old 17 January 2010, 08:22   #9
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I carry a 4 bladed plastic piranha prop as a spare in the boat, and even have a complete set of spare blades as well.

I was looking for a cheap 'get me home prop' for my Suzuki DT200EFI if I managed to wreck the Stainless 3 blade I use normally, and it was up on ebay very cheap including the spare set of blades.

It was cheap as it was meant for an older Johnson, but I knew I could just skim a little off the back face of the hub in my lathe and it would fit the Big Suzi fine. Think I bagged it for @45.

I've not actually used it much more than testing it fits and moves the boat around, but to me the big advantage is that as a spare the weight if it and the spare blades is a lot less than carrying around a spare ali or stainless prop. That and the cost of course

I've planned many times to fit it and do some longer journeys, but keep forgetting.

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Old 17 January 2010, 08:33   #10
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Quote:
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any good or should I now be looking to get alloy or a steel prop.?
I had a Pirhana prop on a hard boat a while back, one blade got a ding and disintegrated so I tried to get a replacement blade. Someone was selling an aluminium prop cheaper than the blade was going to cost with delivery, so I switched and never looked back. The boat was faster and I felt less vulnerable.

Nasher's idea is excellent, a light weight and easy to store spare.

Also handy if you wanted to try out various pitches, but having done so I think I would go for a metal prop and keep the plastic one in a locker.
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Old 17 January 2010, 09:03   #11
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on bigger engines we found they flex slightly (less pitch) on smaller engine they seem ok, i've got one here from a 55hp suzuki i think
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Old 17 January 2010, 09:57   #12
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50 s

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on bigger engines we found they flex slightly (less pitch) on smaller engine they seem ok, i've got one here from a 55hp suzuki i think
Mines on two 50 hp Hondas.
I have not tried any other blades but I may well some time in the future.

But to replace both of them may cost a few pounds just to find out there in little or no difference .

With both engines going I get 30 knots. with 2 persons onboard.

Can't see me getting much more than that.
But who knows???
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Old 17 January 2010, 10:01   #13
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I've got a plastic prop as an emergency spare too. I lent it to Doggypaddle to try and he says it's absolutely appalling.It'll stay as an emergency spare simply because it comes apart and stows in bits quite easily.
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Old 19 January 2010, 07:26   #14
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new prop delivered in a paddy bag..

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I've got a plastic prop as an emergency spare too. I lent it to Doggypaddle to try and he says it's absolutely appalling.It'll stay as an emergency spare simply because it comes apart and stows in bits quite easily.

Well reading the replies from the forum members seems to me some think there o.k. while Others think there Rubbish.

Maybe i will be able to afford to change them this year.
And then I will know if there any better but in the meanwhile 15. ish for a new blade will have to do for now.

Thanks everybody for your input..
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Old 19 January 2010, 19:04   #15
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I had one of these supplied for a test for a boat fishing mag but it must be 15years or so back. It was a while cos we were using decca not gps.
It was absolutely crap so the mag, in the way that some do, never printed the test which would have upset the advertiser a tad! The prop was for a 40hp mariner and it came with a couple of pitches. One as per the one fitted to the boat already the other blades were plus 2 inches on pitch ( because the prop was so efficient - ) . With the original pitch replacement the motor revved its nuts off at wot. With the higher pitch it was a slug to get on the plane and the wot revs were in excess of those we used to get with the ali prop but the speed was considerably reduced. My conclusion was that the blades were flexing under load, and my opinion was unprintable. BUT could be handy to keep in the boat as a get ya home spare as its light and packs away.
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Old 20 January 2010, 06:57   #16
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I've got a plastic prop as an emergency spare too. I lent it to Doggypaddle to try and he says it's absolutely appalling.It'll stay as an emergency spare simply because it comes apart and stows in bits quite easily.
It certainly was with my setup. i got 36knots with a yam K 17" series at about 5600rpm and now run a 19" K and get same speed at less RPM.
with the plastic prop also 19" it maxxed out at 27 is knots and took a mile to get there.
Superb for a lightweight easily stowable spare though. but as others mention apalling compared to a good SS prop and mediocre at best compared to an average Ali prop.
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Old 20 January 2010, 07:17   #17
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two props

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I had one of these supplied for a test for a boat fishing mag but it must be 15years or so back. It was a while cos we were using decca not gps.
It was absolutely crap so the mag, in the way that some do, never printed the test which would have upset the advertiser a tad! The prop was for a 40hp mariner and it came with a couple of pitches. One as per the one fitted to the boat already the other blades were plus 2 inches on pitch ( because the prop was so efficient - ) . With the original pitch replacement the motor revved its nuts off at wot. With the higher pitch it was a slug to get on the plane and the wot revs were in excess of those we used to get with the ali prop but the speed was considerably reduced. My conclusion was that the blades were flexing under load, and my opinion was unprintable. BUT could be handy to keep in the boat as a get ya home spare as its light and packs away.

My 5.6 adventure 1998 with twin Honda 50 hp Engines 96 ltrs fuel 2 batteries and some other stuff approx 25 kgs Two onboard 30 knots with the plastic props.

I don't know if I would get any more out of it with any other props.??
Anybody think I may get a little more speed ??
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Old 20 January 2010, 07:32   #18
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My 5.6 adventure 1998 with twin Honda 50 hp Engines 96 ltrs fuel 2 batteries and some other stuff approx 25 kgs Two onboard 30 knots with the plastic props.

I don't know if I would get any more out of it with any other props.??
Anybody think I may get a little more speed ??
Got to be worth a try. Do you know anyone who could lend yo a pair?
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Old 20 January 2010, 13:27   #19
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Lend a pair

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Got to be worth a try. Do you know anyone who could lend yo a pair?
Nope.

I ended up buying 3 props when I had another boat just to find out the best prop for the boat.
Two of then nonreturnable.
They went to the well known auction site. Well lost out there.

Parana props do a try it first Again Plastic.

I will leave it now till the summer and then take a look at it.
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