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Old 04 January 2016, 09:42   #41
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Originally Posted by gotchiguy View Post
If you research the Viper prop in general I don't think you will find very much positive said about it, especially for a heavier style boat like a RIB.
I must be the exception to the rule. My setup loves the Viper prop. Granted I've never tried anything else but don't feel the need to as she handles all Sea Conditions fantastically well.
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Old 04 January 2016, 09:59   #42
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Originally Posted by BogMonster View Post
My concern with lowering the engine further is that if the plate is below the transom it'll then be spraying water everywhere, and also will create a lot more drag in the water which will impact fuel consumption.
After discovering I'm running about an inch higher than you. I was thinking that perhaps you should try raising your outboard Stephen, you have nothing to lose apart from a little time and effort. Viper props hate being too submerged (there are some props that have holes in to allow bubbles to flow over the blades), you might find it increases WOT and might improve slip. I have difficulty believing that your setup is significantly different to mine apart from layout/weight distribution but as stated before you can use movable ballast around on deck.
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Old 04 January 2016, 13:34   #43
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Hi Andy, no I did not have the Viper fitted when we crossed to Cherbourg. I had a Michigan Wheel Apollo prop. Much better than the Viper, but I think that there is more to be had. As some have also said, I am keen to try a Rev4, when funds permit.
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Old 04 January 2016, 13:58   #44
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I also ditched the Viper props for Apollo's. Totally different set up obviously being twins but the Vipers just didn't grip well in general, massive difference changing to the Apollo's.
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Old 05 January 2016, 12:16   #45
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Originally Posted by BogMonster View Post
..My concern with lowering the engine further is that if the plate is below the transom it'll then be spraying water everywhere, and also will create a lot more drag in the water which will impact fuel consumption.
Stephen, it's meant to be below the water! It's not an anti-cavitation plate, it's an anti-ventilation plate and its purpose is to prevent air entering the prop from above. To work properly it has to be submerged and the water between it and the prop will be solid. The higher it is, the more you need a prop capable of working well in airated water. Personally, I wouldn't be spending large bucks on a prop which someone has simply heard good things about.

I'm rather surprised that Andy Hightower's boat is so different in performance to yours when weight distribution appears to be the main difference, especially since ribs are genarally good at carying weight forward. Could it just be the Osprey hull is poor when bow loaded as you have it?
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Old 05 January 2016, 13:06   #46
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Could it just be the Osprey hull is poor when bow loaded as you have it?
Seeing as almost every Osprey 5.5 and 5.8 ever sold are in this format and we have numerous happy owners (mainly dive clubs) using these boats in preference over anything else we can guarantee this is not the case.

The 6.2 meter RIB that Hightower is running is longer and is fitted with a different engine with a different gearbox profile to the E-tec. So is not really suitable for comparison.

The Viper prop has proved itself on most of the range we build as a good "all rounder", however clearly in this case it is not providing the necessary performance that Stephen is after and as already recommended a larger bladed cupped prop should give him the extra grip he needs to help lift the bow when trimming and avoiding early ventilation.

The biggest challenge here is that the boat is not nearer otherwise we would be there testing it with him
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Old 05 January 2016, 14:00   #47
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Originally Posted by OSPREY RIBS View Post
Seeing as almost every Osprey 5.5 and 5.8 ever sold are in this format and we have numerous happy owners ......
.....The biggest challenge here is that the boat is not nearer otherwise we would be there testing it with him
A good response and I agree, distance engineering is tricky.
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Old 05 January 2016, 18:18   #48
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My old Humber had the engine mounted quite low (plate below transom) and at any lower trim levels there was a huge rooster tail of spray out the back of the boat. I think if I lowered the engine I'd get the same here.

To be clear, I have no regrets about the boat and would recommend the Vipermax to anybody. I love it, and my only regret in the last five years has been that I'd like to have used it more and gone further but time has been the main thing in short supply!

Distance engineering is a curse with everything in this part of the world, that's just the way it is. On the plus side, I get to play in places like this (spot the Gentoo penguins)
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Old 05 January 2016, 18:29   #49
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Going back to the original post I get the impression the Stephen has been generally happy with his set-up, after all he's run it like that for about 7 years.

I've stated my case for a little "free" experimentation because every RIB and helmsman have different requirements. I hope he finds an improvement with his old prop as making a decision to replacing it becomes a much less of a gamble and thus cheaper.

Can you please report back your findings Stephen, I'm sure we'd all be very interested to know how you get on.
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Old 06 January 2016, 03:54   #50
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Chris has suggested via e-mail that I experiment a bit with the spare Raker prop I have, as that's a cupped prop, and while not ideal in other respects (it has exhaust vents which make it 'slip' to some extent and uses noticeably more fuel than the Viper - 10% or so!) it's a free shot at determining whether a bow lifting prop will make any difference to this specific issue.
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