Prop conundrum

[Richard B]

Originally Posted by Pete7

In fact it would make quite a good article on the effects of different props on a boat.

Certainly would

[Mike C]

OK....

Are we going to have a prop swap on the 23 & 24? If so where? We need quick access to fast water and somewhere shallow and calm to drop our nuts in!

I know Andre is free then too!!!!! Anyone can try my 23" ali!!!!

Mike C

[jwalker]

Originally Posted by Mike C

....JWalker...

Not exactly.... I dropped PITCH size to 21" but the increase was in DIAMETER. This would seem to counteract the pitch drop to produce something that gives about the same WOT revs as my ali.

Yeh, that's wot I said. And I thought you said they only suggested the 19" after the 21" didn't work.

That’s why they suggested dropping another 2" in pitch for the Titan..

Anyway, I reckon you need a 19"or 20" S/S of the same diameter as your alloy one. It depends a bit on the shape of the power curve for your engine.

[Mike C]

Originally Posted by Richard B

I've never read anything on RIBnet or anywhere else to suggest that either a Vengeance or a Titan would perform any better than a Laser II.

My understanding is that the Laser II is a higher rake prop than the vengeance or Titan. Apparently this gives bow lift whereas the other two will tend to give stern lift. Bow lift, they tell me, is a good thing in lightweight boats with outboards but with a heavy diesel engine on the back, the stern lift may be better. Also the extra torque of a diesel may be better with the chunkier Vengeance or Titan.... (In theory)

The Laser II also has a very special device, (called a hole drilled in it) to help reduce cavitation/ventilation.... again useful for high set outboards. The hole should be bunged up for diesels..... apparently!

This mean for high performance speedboats a Laser II would be better…. But I’m not so sure about my 1.2 tons of Humber!

Then again the Laser works OK on André’s boat…. But even he would like to try a Vengeance for curiosity if he’s honest

[Richard B]

Originally Posted by Mike C

Are we going to have a prop swap on the 23 & 24? If so where? We need quick access to fast water and somewhere shallow and calm to drop our nuts in!

Sounds like a good idea to me - I think this will be good for us.

I reckon that any pontoon with a right angle that we can reverse up to will do the job. Any friendly marina, or perhaps somewhere on the Hamble?

My understanding is that the Laser II is a higher rake prop than the vengeance or Titan. Apparently this gives bow lift whereas the other two will tend to give stern lift

This may well explain why we get excessive cavitation from our Titan, as our engine is set quite high.

[Mike C]

Originally Posted by jwalker

Yeh, that's wot I said. And I thought you said they only suggested the 19" after the 21" didn't work.


Anyway, I reckon you need a 19"or 20" S/S of the same diameter as your alloy one. It depends a bit on the shape of the power curve for your engine.

Thanks Jwalker,

Yes, that's why I originally wanted a 21", 2" down from my original. I didn't realise the extra diameter would negate the drop in pitch. It really is an impossible thing to get right without trying them! That’s the attraction of the Vengeance to me. It’s the same diameter/size as my ali one so I hope 2” off should give me that 400revs!

Mike C

[Hightower]

Originally Posted by Richard B

Pete - IIRC you once mentioned that Lee Fairweather keeps them in stock? If so I might be able to pick some up one lunchtime.

You gonna buy spacers just for a trial?

[Richard B]

Originally Posted by Hightower

You gonna buy spacers just for a trial?

Yes!

I don't anticipate them being more than a couple of quid each... I keep a standard set on the boat along with a couple of split pins so I can change a prop at sea without risking dropping the only ones on board!

[Pete7]

Originally Posted by Hightower

You gonna buy spacers just for a trial?

I have one or two going spare at the moment, but most should fit, just not sure about Richards Yam, still only one way to find out.

Suggest you launch at Saxon/Drivers Wharf's as tides are mid day and use the slip at Hythe opposite to change the props. Top end of Southampton water has a good area for speed testing.

Pete

[Mike C]

Originally Posted by Richard B

Sounds like a good idea to me - I think this will be good for us.

I reckon that any pontoon with a right angle that we can reverse up to will do the job. Any friendly marina, or perhaps somewhere on the Hamble?

OK, well I'll be in touch later in the week and maybe we can get a few other people to do a real prop swop! High water is 11:38 BST at Portsmouth on the Saturday. Not quite maximum spring but close The Hamble sounds OK... I would like somewhere shallow to stand behind the boat though.

Anyone else coming? - maybe we should start a cruise thread??

Mike C

[Pete7]

Originally Posted by Richard B

Yes! I don't anticipate them being more than a couple of quid each...

Correct, about 25 couples to be exact (£50)

[Hightower]

We talking about behind the prop (thrust washer) or in front of. I ask because Lee quoted me £25 for a thrust washer as a spare, that's unbelivable!! If you want and you'll have to get in fast (off to Austria next week), I could turn you up a thrust washer/s of any thickness in mild steel, with a lick of spray paint would be OK for the weekend wouldn't it?

[Richard B]

Originally Posted by Mike C

I would like somewhere shallow to stand behind the boat though.

Is this because the Alpha One doesn't lift up very high?

Pete - Saxon probably good as they have pontoons ar right angles. Isn't Hythe slip a bit green though - don't want to send Mike A over T!

What we need - in an ideal world - is a slip with a pontoon immediately alongside. The best I can think of is the slip in Yarmouth Harbour.

Andy - £25 is a bit steep, innit! My spare wasn't that much. Great offer of yours, only I don't know the dimensions of what we want!

[simmons0]

Originally Posted by Mike C

Anyone else coming? - maybe we should start a cruise thread??
Mike C

We'd be interested in trying a Laser 2 in 23 inch pitch if anyone has one.
Not sure if we could make it that weekend though.

Mike what does yours rev to with the ali?
And what are you hoping for as a max?

[Hightower]

Pete would know the dimentions, Only really want to O/D, I,D and then I'd make several spacers of different thickness, would be helful if someone knew roughly what thickness and I'll take it from there. Can't do splines though!

[Mike C]

Originally Posted by simmons0

We'd be interested in trying a Laser 2 in 23 inch pitch if anyone has one.
Not sure if we could make it that weekend though.

Mike what does yours rev to with the ali?
And what are you hoping for as a max?

The 23" ali was getting to a maximum of 3,800 rpm. The 21" Titan did do slightly better at 3,900 but the recommended WOT for the Merc 1.7 is 4,400. The boat was fairly heavily laden... ie full of fuel but the week earlier I had 5 people on board... and a full tank. I didn't check the revs then but it was very laboured then!

Gents.... and Loiuse....

I must bail out now... Early start in the morning, but lets see if we can have a good prop swap the w/e after next!

Miike C

[Mike C]

Originally Posted by Richard B

Is this because the Alpha One doesn't lift up very high? YES!

Pete - Saxon probably good as they have pontoons ar right angles. Isn't Hythe slip a bit green though - don't want to send Mike A over T!
NO!!!!!!!

What we need - in an ideal world - is a slip with a pontoon immediately alongside. The best I can think of is the slip in Yarmouth Harbour.
GOOD IDEA

Andy - £25 is a bit steep, innit! My spare wasn't that much. Great offer of yours, only I don't know the dimensions of what we want!

I HOPE THERE IS A CHEAPER WAY!

GOOD NIGHT

[simmons0]

With our standard 23 inch ali the engine will just about over rev with a light load, past 4,400rpm so were looking for a new stainless to bring it down a bit.
We were advised that the laser 2 is usually for petrols, but this is quite a high reving diesel so i think it should be fine.

Goodluck, and let us know what you decide on.

[Richard B]

Originally Posted by Hightower

We talking about behind the prop (thrust washer) or in front of.

AFAIK we're talking about the tapered (thrust) washer between the prop and the gearcase - Pete?

Here's a picture of my spare - for Yam prop on Yam engine.

[Richard B]

Originally Posted by Mike C

lets see if we can have a good prop swap the w/e after next!

Miike C

OK catch you later. I just suspect that we may be limited to swopping between similar engine types.