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Bigplumbs · 23 June 2019, 04:01

I see a lot of people messing with props spending a lot and achieving very little if you are getting the performance you state I would stick to the one you have

Pikey Dave · 23 June 2019, 08:49

Quote:

Originally Posted by Poly

OK, blood sugar recovered...

So everything came together today for a fairly calm water test.

WOT, well trimmed she's sitting at bang on 5750 RPM, and my phones says we maxed out at 26.0 knots (inland water - no tide) with a 9.9x11 aluminium prop. Gearbox ratio is 1:1.92 so I make that a < 10% slip, so I'm happy with that. The recommended rev range is: 5250-6250. So its probably about as good as I am going to get (not that I'm complaining) with a 3 blade aluminium prop.

This was measured in pretty much the lightest load she will ever see (it might be 50kg lighter but nothing more than that for any real time).

It will be used with about 100kg more weight on board (and v. occasionally 150 kg).

I don't know much about stainless and or 4 blades so would I see any benefit (whole shot is fine in todays loading too) from?

S/S 4 blade Solas 10x10 looks like its about £220 delivered by the time its imported from the US.

I can get a "POWERTECH SRA" 10x10 that would cost a bit over £300 delivered from Oz.

Aluminium 4 blade Solas "Amita" 10x11, about £100 delivered

Or do I just stick to standard to standard issue 3 blade ali props at c. £100 each. I'd generally take a spare prop on any long trip / week away so I'm not stuffed if I find the bottom the hard way. So a purchase is forth coming either way.

Re props: leave it for now & see how she behaves in less than ideal conditions with some load in her. Props are like tyres on a car, the limitations/benefits tend to show in the extremes.

Poly · 23 June 2019, 08:53

Quote:

Originally Posted by Bigplumbs

I see a lot of people messing with props spending a lot and achieving very little if you are getting the performance you state I would stick to the one you have

Says the guy with six boats!

However that’s always been my approach in the past - but I’d like to understand from those who understand prop tuning to see what might come from it. The point is I’m going to buy another prop anyway as a spare so can deviate from the stock one (which the dealer fitted by guesswork).

Pikey Dave · 23 June 2019, 09:05

Quote:

Originally Posted by Poly

Says the guy with six boats!

However that’s always been my approach in the past - but I’d like to understand from those who understand prop tuning to see what might come from it. The point is I’m going to buy another prop anyway as a spare so can deviate from the stock one (which the dealer fitted by guesswork).

You should be able to buy Solas props off the shelf from Steel Developments, or was the US import cheaper than them?

Poly · 23 June 2019, 09:17

Quote:

Originally Posted by Pikey Dave

You should be able to buy Solas props off the shelf from Steel Developments, or was the US import cheaper than them?

They need to work on their SEO - google didn’t suggest them! Same price.

Fenlander · 23 June 2019, 10:01

Just take care with a Solas. Loads of folks have them and they get on ok but a few years back we bought one for a Mariner 15 2-stroke and it degraded the performance... not speed as such but ventilation and that slipping feeling on the plane. I had a direct comparison with the OE Quicksilver as it was the same dia and pitch three blade Ali. Looking at them side by side the Solas had a noticeable difference in blade shape. Give Steel Developments their due they accepted the problem and replaced with a new Quicksilver one.

jeffstevens763@g · 23 June 2019, 10:01

Looking at the figures you could pitch up but top end speed wont be a lot more IME but you will loose some scope for change in conditions and weight personally i would stick with what you have and upgrade to a stainless which are suposed to be 5% more efficient then theres the risk if you hit the prop gearbox wise it that bothers you also look at for the price of stainless you can get two ali props more scope pitch wise then.

jwalker · 23 June 2019, 10:12

Leave it as it is until you've done more time with it. If anything you'll need to pitch down, more load, head sea, head wind etc.

Remember, 4 times the power to go twice as fast. Work that back to the extra power you reckon you'll get from a simple prop change. Bugr all!

jeffstevens763@g · 23 June 2019, 10:21

I agree leave until you get the correct loading, conditions. for info i lossed 2knots pitching down from 11 to 10 inch pitch but the performance in the rough keeping on the plane is outstanding with the 10 i put a 12 on and saw no increase in top end but its sluggish ok as a spare though

Limecc · 23 June 2019, 16:39

Quote:

Originally Posted by jeffstevens763@g

I agree leave until you get the correct loading, conditions. for info i lossed 2knots pitching down from 11 to 10 inch pitch but the performance in the rough keeping on the plane is outstanding with the 10 i put a 12 on and saw no increase in top end but its sluggish ok as a spare though

I'm trying to understand the science. Wouldn't you have achieved similar with a four blade 11? I'm considering a prop change myself in fact probably the same or similar to what Poly gets. Same speed, revs and engine. Poly can buy first though 😀, don't put it off too long Poly.

jeffstevens763@g · 23 June 2019, 17:05

Quote:

Originally Posted by Limecc

I'm trying to understand the science. Wouldn't you have achieved similar with a four blade 11? I'm considering a prop change myself in fact probably the same or similar to what Poly gets. Same speed, revs and engine. Poly can buy first though ��, don't put it off too long Poly.

https://www.propeller-shop.eu/propeller-info/

The problem is it's not an exact science four blades will give more thrust at the expense of speed three blades will give you more speed a few years ago I bought a yam 60 high thrust engine for a pilot house fast fisher the supplier loaned me a series of props so I could test on the same day in the same conditions to get the optimum the best way but not always available to all. In polys case he's getting good figures with his load but 100-150 kg more might throw them out of the window in terms of speed and response but he might be happy with that for the few times he has that load or he could come down a pitch or two and only use that prop for the extra weight and as a spare. IMO the prop you use has to be able to perform in all circumstances on a trip not much chance of swapping out whilst at sea so propping for that extra knot at WOT is only any good whilst at that speed bit like 6th gear in your car IMO
Some good info in the link

Pikey Dave · 23 June 2019, 17:30

My previous RIB was a 6.4 RC with twin 115 etecs. It came with BRP 3 blade props. Fantastic in a straight line on flat water, but put it in some rough stuff or tight turns & the props blew out, lost grip & ventilated like crazy. No amount of trimming, engine raising/lowering made any difference. I was advised to try the Mercury Rev4 props by the legendary Mike Vincent at South Coast Marine (bear in mind that Mike is a BRP dealer, not a Mercury dealer, so was plugging the opposition’s product) The difference was night & day, not just an incremental change, more like a quantum shift. I had a similar issue with the current 545, the stock Suzuki prop would lose grip in the rough & ventilate on landing after “taking air” the Solas 4 blade cured all that at a stroke. You wouldn’t put cheap tyres on a Ferrari, so why compromise on the bit of the boat that actually connects you to the water?
The trade off by going 4 blade is a bit off the top speed & a slight increase in fuel consumption, but that’s a price I’m prepared to pay.