Choosing a prop

[Smagu]

Replacing the prop on my 1987ish Yamaha 80hp on the back of a 5.3m Humber rib as it’s a little beat up.

Prop was a spare someone gave me so may never have been the correct one.

13 1/2 X 15-k. Would power me along at 36mph flat out. (No rpm gauge)

Looking for a prop with good torque not overly fussed if I loose some top speed.

Should I replace like for like or try something new?

[Limecc]

Originally Posted by Smagu

Replacing the prop on my 1987ish Yamaha 80hp on the back of a 5.3m Humber rib as it’s a little beat up.

Prop was a spare someone gave me so may never have been the correct one.

13 1/2 X 15-k. Would power me along at 36mph flat out. (No rpm gauge)

Looking for a prop with good torque not overly fussed if I loose some top speed.

Should I replace like for like or try something new?

I posted this earlier today and it's applicable to your engine, so I converted the units to mph.

Pitch/Speed (mph)
15" = 35.2
16" = 37.5
17" = 39.8
18" = 42.1
19" = 44.5
20" = 46.8

You could consider a four blade which would reduce slip and give better response at mid rpm's compared to a 3 blade. Your 15" pitch seems a little small, I'd expect it to be at least 17" but others can give a more reliable answer. You really need a tach to work out whats going on. Also best to optimise engine height or you may find yourself buying an underpitched prop.

[Smagu]

Originally Posted by Limecc

I posted this earlier today and it's applicable to your engine, so I converted the units to mph.

Pitch/Speed (mph)
15" = 35.2
16" = 37.5
17" = 39.8
18" = 42.1
19" = 44.5
20" = 46.8

You could consider a four blade which would reduce slip and give better response at mid rpm's compared to a 3 blade. Your 15" pitch seems a little small, I'd expect it to be at least 17" but others can give a more reliable answer. You really need a tach to work out whats going on. Also best to optimise engine height or you may find yourself buying an underpitched prop.

Thanks so much this is exactly the kind of thing I was looking for!

[jonp]

Its not quite that simple as buying a higher pitch and going faster, don't be mislead by those figures.

Your engine won't simply continue to happily reach full rpm everytime you increase pitch and if the engine can't reach its full rpm or very close to it you can easily put to much strain on it just like trying to drive up a very steep hill in 5th gear at low speed in an underpowered car.

First I would be looking into getting a device to see what rpm you are currently achieving, without this you are stabbing in the dark and possibly harming the engine if you prop incorrectly. If the engine isn't hitting the rev limiter at full rpm you would have an idea that its not underpropped at least.

The size of the boat and power of the engine I would of thought that one you have or possibly a 17pitch is about on the mark, depending on manufacturer.

Props aren't equal and even though I do like the genuine Yamaha aluminium props (that are pretty cheap) I don't rate the stainless as well for the considerable extra cost.

As a comparison I have a 17 pitch stainless yam prop which is nowhere near as good at all round performance as the same size and pitch solas. The funny thing is both of those stainless props aren't anywhere near as good as a 4 blade cheap turning point hustler.

In the past Ive always bought high end stainless 4 blades but was willing to give this cheap a try and have to say on the current boat its excellent.
1 smoother at low speed
2 faster hole shot (take off) vented for fast take off
3 gets the boat on the plane and holds it there at lower rpm
4 better at keeping rpm in big seas
5 better fuel economy
6 surprisingly better top end speed
7 smoother forward reverse changes due to aluminium being so much lighter
8 didn't have to lower pitch which Ive normally done going to 4 blades
9 low cost, less likely someone will steal it!!!
10 hub kit means I can have spare props without needing more hubs, again cost effective.
11 less chance of damaging gearbox if it hits something compared to stainless
12 lifts the stern for a better ride in rough conditions


The downside

1 Not shiny
2 easier to damage if I hit bottom (which Ive never done in over 40 years)
3 ummmm struggling here to come up with anymore!!!!!

[paintman]

Originally Posted by jonp

.
Lots of interesting and tempting 4 blade prop info

I wish you hadn't posted that.
I'll now be spending hours researching 4 blade ally props......

I fitted a 3 blade stainless a couple of years ago & whilst I'm happy with the general performance I'm less than happy with the clunky noises when engaging gears!

I'm assuming you went for the 17 pitch Hustler?

[jonp]

Originally Posted by paintman

I wish you hadn't posted that.
I'll now be spending hours researching 4 blade ally props......

I fitted a 3 blade stainless a couple of years ago & whilst I'm happy with the general performance I'm less than happy with the clunky noises when engaging gears!

I'm assuming you went for the 17 pitch Hustler?

Yes 17 pitch hustler. I did have a solas Amita 4 on the boat I recently sold which wasn't anywhere near as good and before that I had a few 4 blade stainless solas props. I had been looking at getting a stainless 4 blade merc prop but there was a shortage of them which is why I gave the hustler a try. Normally Ive had to drop down a fair amount in pitch when going to 4 blades but not with the hustler.

[paintman]

Thank you.
Currently running a Laser 2 21p stainless which is fine.
Looking at the TP aluminium 4 blades they go to a 21p & I can use my current hub.
Interesting blade configurations.
As you say, they are cheap so for what it costs I may well give it a try.

[Limecc]

Originally Posted by paintman

Thank you.
Currently running a Laser 2 21p stainless which is fine.
Looking at the TP aluminium 4 blades they go to a 21p & I can use my current hub.
Interesting blade configurations.
As you say, they are cheap so for what it costs I may well give it a try.

I'm of the same opinion. Currently using Solas stainless 4 blade which I'm very happy with but looking for something higher pitched for when I'm alone on a voyage.

What's the cheapest way to get one of these props in the UK?

[paintman]

Google for Uk sellers shows Streamlined propellers in Lincolnshire.
TP's own US website shows ^^ plus Aquatec in Lancing and Propeller Revolutions in Poole.

Streamlined's pricing only shows inclusive of hub then plus VAT plus P&P.
£140 + VAT = £168 + p&p.
Don't know if they will do one without the hub which I don't need as I've got two Mercury Flo-Torqs already which TP's website says are fully compatible.
Will contact & see what they say.

Ebay purchase from the USA using ebay's Global Shipping Programme which claims that all charges & duties are paid at time of purchase shows for me as around £116 for just the prop.
I've never used GSP so don't know if that's the reality & that there will be no nasty surprises from the VATman!

Ebay's 'help' and 'contact us' are entirely unhelpful so if anybody has used it for USA to UK your advice would be appreciated.

[Matt]

I've used the GSP loads of times - last time was for my XR Bravo Upper gears, over 1K cost for the gears. (Rebuild thread is on here somewhere)

Works well, simpler for you as the customer because you know what you're paying upfront and I think simpler for the seller too.

No extra fees at all, although delivery times are a little longer than direct shipment.
I prioritise vendors using the GSP now over those that don't.

[Limecc]

TP don't do their dual geometry four blade for a 3.x" gearcase so that rules it out for me. They only do a 3 blade coming in on ebay for under £100 delivered, all fees and import duties paid. Problem is my Solas hub's not compatible so it adds another £50. Might just get a 3 blade Rubex which is, and Steel Developments give a free adjustment so I'll not be disappointed with the pitch I select. Difficult to decide.

Edit: Streamlined Propellers coming in at £85 inc hub kit so how can I go wrong? I wonder if the 3 blade TP is as good as Solas Rubex? Diameter is larger for the latter.

[paintman]

Originally Posted by Matt

I've used the GSP loads of times - last time was for my XR Bravo Upper gears, over 1K cost for the gears. (Rebuild thread is on here somewhere)

Works well, simpler for you as the customer because you know what you're paying upfront and I think simpler for the seller too.

No extra fees at all, although delivery times are a little longer than direct shipment.
I prioritise vendors using the GSP now over those that don't.

Brilliant. Thanks very much.

[Smagu]

Replacing the prop on my 1984 Yamaha 80hp on the back of a 5.3m Humber rib as it’s a little beat up.

Prop was a spare someone gave me so may never have been the correct one.

13 1/2 X 15-k. Would power me along at 32mph flat out. Roughly 6300 rpm 2 passengers and 60l fuel.

Looking for a prop with good torque not overly fussed if I loose some top speed. Most use it for fishing and some knee boarding.

Should I replace like for like or try something new?

[Roflhat]

I'd go for the same pitch again, any lower and you'll be over revving at WOT. A 15k in decent condition will probably drop the rpm a touch anyway

[Smagu]

Sorry to try and revive this thread but was getting some great advice. So it seems my newly fitted rpm gauge was off.

I installed a new one and got a digital tacho which enabled me to calibrate it at various settings up to 3000rpm after this the gauge struggled to pick up rpm.

So maxing out the boat with the current prop I can get 34mph with 2 people and 60l fuel. Sitting at about 5200 rpm.

I am debating getting this 4 blade

https://www.specialistsmallcraft.co.uk/products/13-x-17-k-polastorm-4-1-4-gearcase?variant=31721810428002&currency=GBP&utm_m edium=product_sync&utm_source=google&utm_content=s ag_organic&utm_campaign=sag_organic&utm_campaign=g s-2020-02-04&utm_source=google&utm_medium=smart_campaign&gcl id=CjwKCAjw9qiTBhBbEiwAp-GE0cFAfDEdKkjGqLOQMlLveiLVMl0Wm9Jj_mZhJWvikzDg1osy XiShFxoCtFYQAvD_BwE


I thought getting a prop would be an easy decision!

[Jung at Heart]

@smagu
Mark at specialist small craft can advise you on the best prop size for whatever you are looking to achieve, I recommend giving him a call and discussing it before buying the 13 x 17K 4 blade.

I've just bought a 13 x 15K 4 blade for my Yamaha F50 high thrust outboard on my C-Fury, it's replacing a Yamaha 13 x 17K 3 blade prop, I'm not trying it until next week so can't give a comparison.