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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?

Quote:
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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