Hello Sea tigers,

currently having 2 blades 16"x11 prop and struggling to get to 5.5 knots. Hull is clean. Engine 1200 hours works like a Mig 29 engine.

Austral and Porters are selling me 3 blades 16x11 or 15x13. Porters is for 16x11 Austral more for 15x13. Both are around 1500 bucks. I have got in touch with some sea tigers in USA and they are having a completely different idea. They are talking about cup dimensions .040, .060. Their suggestion is 15x9.5 with some cup dimensions introduced. I am forwarding the explanation. Any opinion is appreciated. The price is sexy.
Thank you tigers


Hi and thank you for your patience. The engineers sent me this below and have come up with a good propeller for you: Mr. Kirk,To give you a quick reason behind our decision:Going from 2 blades to 3-Blades is like adding 1" diameter.And going from .40 DAR to .60 DAR is like adding 2" pitch.And going from zero cup to .045 Cup is like adding 1" pitch.This means that in the current "2-Blade language" our 15 x 9.5, 3-Blade, .045Cup, .60 DAR, Acme part number 2996 equates to a 16 x 12.5, 2-Blade with zero cup. We recommend the propeller below:www.myinboardmarine.com/collections/propellers-inboard/products/2996-acme-3-blade-propeller-1-bore-right-hand-weke-ski-15-00-x-9-5?_pos=1&_sid=ee77da9cb&_ss=r Please let me know if you have any questions and thank you much! Kind Regards & Blessings,

Donald C. KirkCEO | My Inboard Marine, LLCMobile: 803-766-8586
Email: [email protected]
MyInboardMarine.com"YOUR Inboard Marine Source!"

I would suggest sticking with 5.5 knots and having an extra cup of coffee.

Woko and others thanks for you messages.

To be honest with you, it will take a long time to get use to race this tank. This boat is new to me. Its big and heavy. The reason why I want to change the prop is the fact that is slow, very very slow. 5 Knots is not a good speed and I don't want to run my engine on 3300 rpm's non stop. Engine is 3GM 30F, gear ratio is 2.62. Porters is thinking of 16x11, Austral 15x13. Both are promising the hull speed which is around 7.4 knots at 3200/3300rpm's. Waterline is 9.4m. At 2600/2800rpm speed should be 6.8knots and 3000 rpm should pull 7 knots.
Cruising at 6.8 knots at 2600 rpm would be a sweet spot. Diesel consumption and engine will not suffer much and will hopefully last. It's a bit painful to hear engine screaming and boats is slow. Deja vu? Maybe, but when 11m Hunter moves slowly then 8m Tasman than we have a problem.
The good thing is kids and wife are happy. No iPads on weekends and that is the main thing. Happy days!

Thanks,
the point is to keep the engine for another 20 years. So why not cruise at 6.8 knots / 2600 rpm instead of 4 knots at the same rpms. It's about fuel efficiency. When school holidays comes that will be two to 4 weeks of motoring my friend. Pittwater and god knows where else. Batman's bay???It makes a big difference at the end of the holidays. This tank is not a sailing machine, but I have achieved 11 knots selling on identical boat with 3 blades prop. It all depends if you pick right winds.

In a nutshell, it is worth to upgrade to 3 blades. Benefits are huge and a little bit of extra drag won't change much.

I would say 80% of people that buy sailboats should have bought a motor boat. Thank god they don't because there would be even more motor boats screaming around.
Unfortunately I had a quick look at some Hunter 356 owner sites and it does sound like 6+ knots is the norm for motoring. Of the 5 or 6 I read nobody talked about sailing speeds or what changing the prop did to sailing speeds.
Like most things in life you get what you pay for. As others have mentioned that looks like a motor boat prop. Do some research.
A good folding or feathering prop will give you similar motoring speeds and have a huge difference on sailing speeds. At least 1 knot. It will cost you 3 times as much though.
If you say I am happy to loose 1 knot of sailing speed to be able to motor faster you don't get sailing. The slowest most expensive way to get somewhere for free!
I have worked on lots of different sail boats and as shaggy said 5-6 knots is a respectable motoring speed.
Have you tried motor sailing you can easily add 1 knot of boat speed. Even if you don't go faster it can reduce fuel consumption a lot.

We have 2 Bruntons props. The 3 blade Auto prop, I think that's the H6 and the 2 blade folding. Difference for motoring and sailing is huge.
Keep the 3 blade well greased and clean so the blades can turn freely.
Maybe look at a service kit in the UK. Might be cheaper even with shipping etc.
When motor sailing pointing high like you said try putting a reef in. If you get the outboard end tight and a nice flat main you can point higher. Less heal too. Especially if you have an old main that's a bit full in the foot.

I personally don't think you will get much better than 5.5 knots even with a three blader. The windage and hull shape in a seaway will be the limitation with a Hunter 36.
If you want to spend money then I would suggest a Volvo 3 blade folding propeller. This will give half a knot improvement in sailing performance and should be more than adequate for motoring. You can still motor sail if needed.

It seems Porters think you own a fishing boat.

Mate, My Daughter has a 64 foot dinghy . You should have got one instead. Cant hear the engine at all under 20 kn. , top speed 34kn, gyros to level it out in rough water, set gps to whatever and boat stays in one position without anchor, swim platform lowers underwater ,transom lifts and out pops a tender. Your misses will love it and you wont have to worry about that extra knot.

Hey Tiger Serb
Where are you motoring to that your in such a hurry?

The extra knot your chasing would put you about 1600 meters ahead of where you are after about an hour of motoring flat out (like a stink boat)

The extra knot will put a bigger hole in ypur boat when you hit a reef, jetty, moored boat.

Im thinking its all about small boat syndrone.

Maybe your boat just isant big enough.

And id think it best to not bin, sell, give away the prop that is propelling your boat now as the next owner (if you can find one thats not on seabreeze) will most likely want to re install it so the boat sails faster (with your you brute antifouling)


Cheers and good luck

PS..... catamarans dont tip to 37 deg, but maybe you can prove me wrong

Jolene said..
If it's what you want to do just do it, change the prop
No one is really going care. No one is buying it for you .
Watch Porters though, the last prop I seen from them was terrible

Have to ask, was the prop returned to them to enable rectification or just whinged about aimlessly?

Jolene said..
No, the prop wasn't returned as I was able to fix the problem and I don't recall the customer whinging aimlessly about it.

Glad you fix it. Going to see Warren at WB Marine in Wollongong. He is cheaper and I like the bloke. Its not only a knot difference, yesterday went to cruise a bit around the harbour and prop has some serious issues down there. Vibration and noice is painful. Ended up cruising 3 knots on 2400 rpms. This is a nonsense. It should be 6 knots on 2400 rpms.Tomorrow morning taking the prop off and heading down to Wollongong. I just can not figure out what would be the best option and quieter cruising, 16x12 or 15x13 in 3 blades? Even if I am cruising with family and friends around the Harbour all day slowly it will be done on 1500 rpm not on 3000. I hope you get the point. 4 knots and happy days. In terms of sails, got the quote 3700 USD for main and Genoa (uv protection) from Far East sails (Chinese) in Dacron. That would be under 5.5k in AUD. I consider this as a good price.

Any suggestions in regards to prop is appreciated.

UncleBob said..

Jolene said..
No, the prop wasn't returned as I was able to fix the problem and I don't recall the customer whinging aimlessly about it.

So you feel the need to adversely comment here on a product manufacturer that you feel didn't live up to expectations, without even giving the company the opportunity to remedy or at least comment on the problem. Fair enough if they had blown you off, fire away, but really??
Good that you were able to fix it, does the prop perform as expected now?

It wasn't my prop. I have no idea what conversations the owner of the prop had with the company and I don't care. The customer asked me to fit his brand new prop .
I can say what ever I want about it, and its my opinion that the propeller should never been sent, no excuses.
I fitted the new prop after some machining, and it worked, that's all I know about it.

You are way over propping the boat. My S&S34, 6.5 tonnes, had a 20hp engine with a 15 X 10 two bladed folding Gori prop. I bought it from Porters to replace the worn out 15 X 9 that was on it. Porters were fantastic in their advice and the prop was exactly right.
The 15 X 10 pushed the boat at 7 kts (hull speed) at or near max rpm. She cruised at 5.5 kts at 2200rpm. If you overload the engine with a big prop you will go slow, use heaps of fuel, and have lots of unburnt fuel coming out the exhaust to make the cockpit uninhabitable.
Assuming you have a 20 bhp or so engine a 15 X 10 or maybe a 16 X 9 two bladed prop is what you need.

As others have said, a ski/wakeboard prop is a completely different beast to a yacht prop.

A fixed three bladed fixed prop will cost you about a knot in sailing speed; from a British magazine test, "at 5 knots, a fixed three-blade prop with its shaft locked creates almost half as much drag as the entire hull". If you don't want to heel the boat too much, you'd be better off with a good folding 2-bladed prop. That way the boat will create less drag under sail so you can go a lot faster with less sail up.

You don't need better sails before getting a folding prop, since even an in-mast furling main, well trimmed, won't cost you a knot. A Hunter 365 with three-bladed prop will sail slower than a good Tasman 26.

woko said..
And the other issue with over propping, that is if you have the power to swing it is idle speed is fast, mooring / docking becomes a bit more of a
fwd astern dilemma with associated prop walk too boot

Yes, but vastly entertaining for spectators at the slipway!

MorningBird said..
You are way over propping the boat. My S&S34, 6.5 tonnes, had a 20hp engine with a 15 X 10 two bladed folding Gori prop. I bought it from Porters to replace the worn out 15 X 9 that was on it. Porters were fantastic in their advice and the prop was exactly right.
The 15 X 10 pushed the boat at 7 kts (hull speed) at or near max rpm. She cruised at 5.5 kts at 2200rpm. If you overload the engine with a big prop you will go slow, use heaps of fuel, and have lots of unburnt fuel coming out the exhaust to make the cockpit uninhabitable.
Assuming you have a 20 bhp or so engine a 15 X 10 or maybe a 16 X 9 two bladed prop is what you need.

Read your post, gave another call to Austral and David did the calculations again. His words: 15x13 in 3 blades fixed will be a bit too much. 15x12.5 will be perfect for 29 hp. so you are not too far 20 hp = 15x10.