Hello brothers,

Need a new propeller for my Tasman 26. The old one is out of balance and it's a wrong size. Been recommended to get a 15.5 x 12 by Austral. They are asking 1200 bucks for it.
Did anybody changed a propeller on the same engine to get 7 knots (max full speed). Should I get a bigger pitch?
What do you guys recommending? I don't mind to overpitch a bit as long I can achieve a bit better speed.
Before I spend 1200 bucks at Austral maybe you can give me some advice based on your experience of yours so I can buy a different size propeller and achieve better speed for the same money.

I do believe to Austral engineers but they also told me that Max hull speed of my boat is 6.5 knots but I have achieved 9 knots (17 km/h speed of ground) with my boat sailing under high speed wind around the Shark Island in Sydney harbour..

As soon as I get some suggestions based on testimonies I will pay a diver to remove the old propeller and jump to peakhurst to get a new propeller and once the new prop is on bost is going to be antifuled and prop speed will be applied and that eill definitely make a difference ( current max speed is 4 knots and lot of vibrations under high revs)
Please see photo of the old propeller

Thanks

The first consideration is to forget about exceeding 6 knots in a short beamy yacht motoring!
I would suggest taking the propeller off and taking it into Porters for a tune-up. Porters will balance the prop and add or remove metal if required and alter the pitch if required. If there is vibration when running it's very likely the shaft has a bend. Pull the shaft and take it into Porters with the prop and don't use a hammer to remove the prop! When reinstalled and back in the water realign the engine and shaft and if you make 5 knots through the water in the harbour be satisfied.

Theoretical hull speed is the speed a vessel can make before she starts to climb her bow wave, which in turn causes exaggerated effort to gain more speed. When under sail the hull shape presented to the water is changed due to heeling this can improve hull speed, more importantly the sails are capable of generating more power than the engine. Also ground speed makes no allowance for tidal flows etc. I would be wary of over pitching a prop as it will cause the engine to be over worked leading to overheating and catastrophic failure. You could get a variable pitch prop and adjust it to your preference but they are expensive

FORGET 7 KNOTS under motor!!!!!!

Take note of the above comments.

Serb;

Please understand: you will never ever get your 8hp engine to give you 7 knots (unless you have wind or tide adding to the speed). Repeat, never ever.

In ideal conditions (no wind, mirror-calm, no tide, spotless hull and prop, engine running well, perfectly sized prop) you will get a bit over 6 knots, but not 7. A few of us have said this and you need to listen - not so that we can feel clever, but to avoid you being very disappointed after spending all that money.

There are many prop calculators on line and they will all tell you pretty much the same thing, as will reputable vendors.

Good luck with it, Graeme

Thank you buddy,
I got it. It looks like that an engineer from Austral is 100% correct. 6.5knot is the max speed and I would be the most happy sailor in the harbour if I could fly home to Woolwich from heads at 12km/h with no wind ....Now doing only half of that.

That has been accepted! Now just one more thing boys and I will leave you in peace...
Do I recondition existing old prop like was suggested by some of you or do I go to Austral and pay 1200 bucks and buy new prop. I am planing to keep my little refuge from my wife for long time so maybe 1200 bucks for a long run is not that much money... and webmistress consider that repiching an old propeller will come with thr cost too..

Thanks yous and see you around the harbour. You will ne recognising my boat it is the only pregnant 26 footer with a pirot flag!

Thanks one more time to all your help.

"Do I recondition existing old prop like was suggested by some of you or do I go to Austral and pay 1200 bucks..."

Take Ramona's advice: Take it into Porter's and get a quote from them of your options 1) getting the balancing, pitch and add/subtract metal to the blades, and 2) quote for a new one.
But listen to engineering advice.

Thanks,

An engineer and a mechanic both have sad to get a new propeller because the current one is chiped too much.. but you guys are more honest than someone who needs to sell the propeller and mechanics who takes time to fix it...both mechanic and engineers confirmed your theory of max speed 6.5 knots...
Can not wait to fix the propeller and do the antifuling to be able to fly 12km/h... that is the double cruising speed than I can achieve now!

I let you know the outcome!

If your old prop is not smooth its performance will suffer, and also Propspeed will not work nearly as well (happened to me with my old pitted prop).
One last thing Serb and I promise I'll stop nagging you...... the data from Austral that you posted is based on engine speed of 2200rpm. At 2200 your engine won't develop 8hp, it will be more like 6, and that certainly won't get you up to 6.5 knots no matter how good the prop is. Please get them to check this against rated engine speed for 8hp, which will be around 3000rpm.
Now I'll shut up.

Thanks buddy,

I also found a bit strange that rated my engine 2200 rpm..I actually got in touch with some tiger from Wollongong and he is trying to get the right propeller for the boat. He was surprised when they wrote 2200 but it was maybe a mistake instead of 3200rpm...

Anyway this tiger is cheaper that austral and all my friends are using him for boats and ski jets and so far did the great job for almost half money...

Here in Sydney is raining and my diver will not be able to put the prop off before Saturday but as soon he does it I will make few photos and post it and than ofcourse as soon as a new prop comes from Wollongong we will compare them and speed as well...
It can be a good refrence for future if someone on the forum need more details... if a new propeller comes good I will send you guys a phone number of this tiger from Wollongong just in case.

Take care and try to get some egold crypto and convert them to mex crypto ...hold and in 5 years you guys will be rich...

So as far as I can determine from this post having 10 responses, and your prior post on the exact same topic but with a different subject title having 41 responses, you have gained a written quotation including propeller details and associated advice from Austral Propellers after they were good enough to take on board your enquiry in good faith, and they actioned their extensive professional assessments and responses. You valued their advice and efforts. And now you are going to task another company with the work, they presumably acting on the advice you have gleaned from Austral and which you have passed on to them. With great respect this is very disingenuous and not an act of good faith on your part. I have nothing to do with Austral. If I have missed something in coming to this conclusion please advise.

In all the prior communications of the two post responses, I have not got the impression that you have taken in that a displacement hull boat or yacht type needs a very different propeller than a planing hull boat type. The displacement hull boat type needs a lower pitch, higher blade area and lower revving prop than a planing hull type. There is nothing you can do with revs as that is a given with your diesel and gearbox ratio which have been set up initially to deliver low revs - but you can sort out the low pitch and higher blade area aspects in your purchase decision.

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Serb1980 said..
Thanks buddy,

I also found a bit strange that rated my engine 2200 rpm..I actually got in touch with some tiger from Wollongong and he is trying to get the right propeller for the boat. He was surprised when they wrote 2200 but it was maybe a mistake instead of 3200rpm...

Anyway this tiger is cheaper that austral and all my friends are using him for boats and ski jets and so far did the great job for almost half money...

Here in Sydney is raining and my diver will not be able to put the prop off before Saturday but as soon he does it I will make few photos and post it and than ofcourse as soon as a new prop comes from Wollongong we will compare them and speed as well...
It can be a good refrence for future if someone on the forum need more details... if a new propeller comes good I will send you guys a phone number of this tiger from Wollongong just in case.

Take care and try to get some egold crypto and convert them to mex crypto ...hold and in 5 years you guys will be rich...

And just who is some tiger from Wollongong?

Very confusing with this propeller business.
Austral sad 15.5 x 12 prop
Many others 14x12 prop... One of them is a man called Warren from WB Marine In Wollongong, also known as a tiger.
The idea here is to get some advice from people who had the same problem and to see what is their experience with a new propeller especially with 14x12 and 15.5x12...
This is nothing to do with respect towards Austral or WD Marine. It has to do with my boat performance. If Austral's prop is better for my boat I will pay 1200 bucks instead of 700 bucks at WB Marine.
The difference between two props is huge! How can I know which one to buy... I don't care for 500 bucks difference. I care that prop is not overloading the engine... again spoke with my father who is an engineer buy he works for Merc and obviously has no idea how to help but he told me l: let it rev a bit.. what that suggests is that 14x12 would make the engine a bit more happy ....
If someone on this forum could write his experiences with 15.5x12 prop or 14x12 prop it would help a lot. Both my father (how is not an expert) and tiger from WB Marine thinks that 15 5 x 12 is a bit to much for little yanmar and I am trying to get some of your opinion and experience.
Someone here must have 8hp yanmar and can write about their prop size and performance.
I am not trying to be smart or disrespect people from Austral or anybody else I am trying to fix this issue ones only because divers are expensive and I don't like to waist their time...

I hope you understand my pain.. I am just interested the size of propeller from others if not a secret ofcourse. We are talking about 8hp and around 26f boat...if people could give some example than we can logically conclude which way to go... I am sure that 15 5x12 prop and 14x12 will give different performance, buy which one will perform better to reach hull speed without damaging the engine on the long run? Tiger from WD took long time to calculate the prop size and asked 1000 questions while Austral prople didn't... it doesn't mean nothing but I know that Austral has been there for 50 years....well both got the same pitch 12 which is ok is just the size 15.5 and 14 that differs. Maybe will not make to much difference... any opinion is welcome...

Thank you guys for your help. I appreciate it.

The 15.5 prop may be the most efficient in the calculations,, but can you swing it and if so will you have roughly 15 % of the prop diameter in clearance from the hull?
My boat has a 17" prop but not enough clearance, that causes problems. Next time I haul out I'm going to cut some off the propeller blades

Cool, it is reassuring that somebody got 17inch prop....I will than go with Austral....I was scared most of you guys will have 12inch of something small....
I will ask the diver to measured the distance from shaft to the hull, hupfuly it will be enough space to fit it in.....
Thank buddy

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Serb1980 said..
Cool, it is reassuring that somebody got 17inch prop....I will than go with Austral....I was scared most of you guys will have 12inch of something small....
I will ask the diver to measured the distance from shaft to the hull, hupfuly it will be enough space to fit it in.....
Thank buddy

Just to clarify,
My boat is not a Tasman 26.
My boat has a 30 HP engine.

Ooooooo,
That why I am struggling with this bloody propeller business. If only one person who has 26 footer with 8hp could jump here and write his propeller size it would make my life easier...

I did:

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FabulousPhill said..

Serb1980 said.... Well, prop has 3 blades but I very small. Once I got stuck to neighbors mooring and needed to cut the robe around the propeller and I must say that I was surprised how small propeller really is. ... If feels that propeller is not balanced,...

3 blades (as seen) or 2 blades (in line with the symptoms) could be a moot point, until you dive and clean it again. I would suggest going to a shallow beach area so that you know there are no sharks coming from one direction, so you only have one other direction to look out for. (been there, feared that too). Take gloves and a paint scraper to scrape the propeller clean of barnacles, and you could polish it a bit with steel wool, while under the water.
I had a YSM 8 and the propeller on it was about 12inches diameter. I threw it away with the motor, and regret that now. I would think that your propeller might be undersized and the number of blades also contribute to it not giving full power. I had a 26 foot boat with a top speed of 3.5 to 4.5 knots, because it was also 4.5 tonnes weight/displacement. So all these things, and the shape of the hull contribute to slow speeds. The answer is a clean propeller and clean hull. Then look at the number of blades and the diameter.

in your duplicate post.

Go for a swim, take the propeller off yourself, and follow the rest of the copious advice you've been given. Your boat's hull shape and weight will be different from what I had, so you simply can't put the same propellor on. Get advice.

Ok

If you reckon your Tasman 26 did 9 knots on the harbour then your speedo is wrong, or your GPS is jumping around.

That three bladed prop will be killing your speed under sail.

Porters do good work. They over-pitched my old folding prop on the 28'er ages ago, when it had an inboard, and it worked very well. It's a boat of generally similar shape and weight to a Tasman, although with cleaner hull lines and therefore a higher speed.

I think the prop on that boat is now a three-bladed 8.5" dia 7.5" pitch on a 9.8 hp outboard and it goes really well. The proportionate speed would be at least as high as that of our other boat, a 36'er with three-bladed feathering prop and 20hp diesel.

A three bladed fixed prop on an inboard will kill performance under sail. I wouldn't bother re-pitching or replacing a three-bladed prop but would go straight to a simple folding one, although you'll have to ensure it's kept clean.

I don't have a propeller that is something that I am trying to explain... have a look at this

Yep. You don't have a propeller.
After all these posts we find out that you have lost a blade.
Would have saved a lot of time to know that a couple of weeks ago.
I wonder how long it has been like that?

So you don't really need a bigger prop.
You need a replacement propeller.

Good luck with your search.

gary

That solves a mystery.
It explains the speed and vibration issue, so less need to worry about vibration elsewhere. It looks a bit small, but that also depends on how much clearance to the hull.
It also tells you the bore size, the propeller diameter, pitch, etc so that a replacement is more straightforward now. It's a lot of progress Serb.

A bit of a difference there. Due to the clearance it will still 12 inch but pitch will increase to 16 to compensate the loss in diameter.... thanks brothers for all your help

Please edit the photo (cropping it) to remove a picture of your bank card.

Thanks

Serb it's good you've found the problem.& it was obvious in the end. You really should get some snorkeling gear

But even with a third blade, this looks like 12x9 propeller. How this propeller can push 3t boat especially the pregnant one like Tasman 26...8hp and prop 12x9 with a kilo of moss on it I am really surprised that my Tasman ( due to be antifuled) moved 6km/h...

Just can not wait Sunday to put back a new prop and go for a spin... that will be sexy.... Hopfuly 11km/h and after antifouling my dearm will come true a full hull speed 6.5knots or 13km/h...
Than I'll be able to run home if needed urgently without motoring 2 hours from heads to Woolwich...

I will post the results,shortly...

Keep in touch my dear friends, and thank you for your kind advices. I really appreciate it..

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wongaga said..
Serb;

Please understand: you will never ever get your 8hp engine to give you 7 knots (unless you have wind or tide adding to the speed). Repeat, never ever.

In ideal conditions (no wind, mirror-calm, no tide, spotless hull and prop, engine running well, perfectly sized prop) you will get a bit over 6 knots, but not 7. A few of us have said this and you need to listen - not so that we can feel clever, but to avoid you being very disappointed after spending all that money.

There are many prop calculators on line and they will all tell you pretty much the same thing, as will reputable vendors.

Good luck with it, Graeme

What Graeme is saying is that even with the correct prop, 8hp will only get you to hull speed in perfect conditions. So you have to think what you need the motor for:
* Getting on or off the mooring to clear water- don't need speed
* Battling against a headwind on a lee shore-pretty important. Here you would be lucky to to achieve 3 to 4 knots with 8hp and a 26ft boat. And this is where you need all the power from the motor that you can get. Power=Torque x speed. So max revs needed. So I would select the prop to give me max revs at 4 knots, and be careful not to over-rev on flat calm.

Correct,
The new prop is just overpitched . All I am getting is black smoke and 2 knots max speed. Really disappointing...after all time and money I have spend ( divers, austral I got 2 knots and the old propeller gave 4 in that horrible state.. )