dear friends,

Recently purchased sailing boat Tasman 26 foot. It has reconditioned 8hp yanmar diesel engine inboard. It's been antifuled 12 months a go. I have booked a new antifuling for 1st of Dec. Now, the issue is that engine is working fine and boat is catching the speed very quickly 5km/h but after that more throttle I am giving speed is only getting to 8km/h but full hull speed it 7 knots (13km/h). I went under the water and checked the prop and hull. They are dirthy.
Now I been told by my father (a Merc engineer in Europe) that once antifuling is done and propeller has been painted with a special chemicals my boat will easy reach 13km/h again.
I am struggling to bealive that dirty hull and propeller can reduce speed from 13 to 6 or 7 km/h. Should I increase the peach of the propeller once the boat is out for antifuling? The propeller is very small, and I must say that a couple weeks a go I had an enormous issue to get back to Woolwich from the Manly especially under the Harbour Bridge due to strong wind against me. I really must fix this issue ASAP. It is scary when you don't have a control over the boat due to the low speed.
Question 1: in your opinion will speed increase significantly once boat is properly antifuled
Question 2: should I pay a mechanic to increase my pitch and make the boat going faster.

Please don't forget that Sydney weather can change fast and every knot counts. In addition, my father told me that if I increase the pitch boat will go faster buy I might have a bit less control over the boat while mooring.

Any suggestions especially from owner of 26f sailing boat with yanmar 1gm10 (8hp) will be appreciated. If any changes have been made what is the propeller size? I don't mind if boat is consuming a bit more of diesel. It's just painful fot cruise 6km/h with screaming engine all day long from Woolwich to Many and back if there is very little wind to push the sails. I just convinced my wife to finally get to the boat buy noise is just to loud to cruise around trying to get max speed of 8km/h. Engine is working fine, no smoke at all unless throttle is fully open. Oil has been changed and engine has been redone a couple year a go.

Thank you my dear friend and see you around Woolwich and Sydney Harbour.

Stay safe.

Yep. Dirty hull will certainly slow you down that much and a dirty prop will also. Imagine thousands of little fingers catching every piece of water as it passes.

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There is no way a Tasman 26 would have a hull speed of 7 knots.







Hull Speed Formula

Theoretical displacement hull speed is calculated by the formula: velocity in knots = 1.35 x the square root of the waterline length in feet.
The LWL is just under 22 feet.

Take a swim and use a long-handled scraper to clear off the blades of the propeller and go for a test run. You should get about 4 knots in flat water and a bit of wind. A dirty bottom will slow the boat but the prop being dirty will have the greatest effect.

It is surprising how much even a little bit of prop fouling will reduce speed. Check the prop against recommended size when you get it on the slip - it's not unknown for a previous owner to have fitted a totally unsuitable prop to save a few hundred bucks (as happened on my boat). Your hull speed will be somewhere around 6 knots, not 7.

Cheers, Graeme

slime on the hull will knock 5 to 10 % off sailing performance a few barnacles on the prop will knock 20 % off steaming speeds a lot 70 % a solid clean will make massive difference a slipping and coat of antifoul even more

Thank you guys, I will antifuled it and try to put a better propeller. Hopefully I will get that bloody 13km/h. Yesterday I got caught from heads towards back on the half way. Max speed was 7 km/h and was raining strongly. Can not wait to antifuled the boat and fix the propeller so I can fly like a jet Mig 29...

Once is done I will update

Hmm 4knots max speed, it doesn't make sense to me because I have achieved 13km/h with my Tasman 26 on the windy day around the Shark Island just using Genoa at one point but to catch 11km/h was easy that day (but it was very windy).. now I can get 4 knots with dirty hull and shocking propeller so hull speed is definitely more than 4 knots. My gps is calculating speed from the ground not from the sea. I am probably confusing you guys a bit with my English grammar. I regret not taking the photo that day when I have achieved 13km/h but it was almost impossible because I was inclined due to wind bending the boat...anyway, as soon as I fix the boat I will let you know. My boat is very wide like an egg and I just don't understand how to calculate the hull speed. I just whent to data base of the boat and it says 7.25kn Max speed....almost bouble than 4...
I will keep you posted till than stay safe

The rule of thumb for hull speed is 1.34 times the square root of water-line length. Forget 7 knots under motor, think around 6 with clean hull, and completely clean correct prop. But add some slime and just a tiny bit of prop fouling and you'll lose around 1/2 a knot. And those numbers are best case, in flat still conditions. But still an awful lot better than what you're getting now!

For boats and yachts suggest best to talk about speed in knots nothing else. The lwl of a Tasman 26 is 21.68ft as per here;

sailboatdata.com/sailboat/tasman-26

The normal hull speed equation as per Wongaga and Ramona is 1.34xsquare root of lwl (in feet) which is 6.24kts for a Tasman 26 - see the 1.34 factor here and in many other links

sailingmagazine.net/article-2211-sailing-breaks-free-of-the-math-that-has-held-it-back-for-centuries.html

So not sure where the above text indicates hull speed is 4kts - all of the above text validly indicates a hull speed of around 6.2kts as far as I can see.

Of course if you are in a 25kt+wind even with just a genoa and beam reaching or broad reaching the wind power resulting will be greater than your 8hp Yanmar so speeds above 6.2kts with clean hull and unfouled feathering or folding propeller set properly for minimum drag are very much expected. Hull speed doesn't mean that will be it - in a 40kt westerly hurtling down the harbour trying to get to safety with your genoa up you should get 7-8kts with clean hull and feathering or folding prop - but you won't get any more than this with that hull design and weight - of course Melges24s get close to 20kts in such winds as they are a very different hull design type and weight.

After afouling and prop cleaning expect you will get 6kts speed over the ground in no wind or tide as long as your prop is effective and your Yanmar is delivering close to 8hp - what is your prop type? If it is a feathering or folding 2 blade prop it isn't designed for getting to full hull speed under power, rather for low drag when sailing. If your reconditioned Yanmar is not delivering 8hp and the associated torque on the torque speed curve then this will be a problem reaching 6.2kts. 8hp is more than fine getting a Tasman26 off the mooring and back in light to medium winds but going against 25+ winds and seas will certainly reduce the speed over the ground as expected.

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r13 said..
For boats and yachts suggest best to talk about speed in knots nothing else. The lwl of a Tasman 26 is 21.68ft as per here;

sailboatdata.com/sailboat/tasman-26

The normal hull speed equation as per Wongaga and Ramona is 1.34xsquare root of lwl (in feet) which is 6.24kts for a Tasman 26 - see the 1.34 factor here and in many other links

sailingmagazine.net/article-2211-sailing-breaks-free-of-the-math-that-has-held-it-back-for-centuries.html

So not sure where the above text indicates hull speed is 4kts - all of the above text validly indicates a hull speed of around 6.2kts as far as I can see.

Of course if you are in a 25kt+wind even with just a genoa and beam reaching or broad reaching the wind power resulting will be greater than your 8hp Yanmar so speeds above 6.2kts with clean hull and unfouled feathering or folding propeller set properly for minimum drag are very much expected. Hull speed doesn't mean that will be it - in a 40kt westerly hurtling down the harbour trying to get to safety with your genoa up you should get 7-8kts with clean hull and feathering or folding prop - but you won't get any more than this with that hull design and weight - of course Melges24s get close to 20kts in such winds as they are a very different hull design type and weight.

After afouling and prop cleaning expect you will get 6kts speed over the ground in no wind or tide as long as your prop is effective and your Yanmar is delivering close to 8hp - what is your prop type? If it is a feathering or folding 2 blade prop it isn't designed for getting to full hull speed under power, rather for low drag when sailing. If your reconditioned Yanmar is not delivering 8hp and the associated torque on the torque speed curve then this will be a problem reaching 6.2kts. 8hp is more than fine getting a Tasman26 off the mooring and back in light to medium winds but going against 25+ winds and seas will certainly reduce the speed over the ground as expected.

Remember the 1.34 is a block coefficient for the hull form. The Tasman may be a little more or less but its a good rule of thumb.

Cool, thank you guys you are all legends, got the idea now. 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. I have feeling that engine is making too much revs it really screms..... actually it is very quite on low speed 5km/h but after that noice is 4 times bigger but speed is just increasing to 7km/max. If feels that propeller is not balanced, very strange feeling I wish you guys can experience that. It is very difficult to explain in words. I am scared of sharks otherwise I will go and take measurements of propeller. Here is the photo from last year while putting copper oxide on it.

Forum does not allow me to post the picture of the prop because I am a new member of the forum.??

I gave an Austral a call and they told me that I can achieve 6knots speed with 15x12 propeller and it will cost me $1200.

Question for you experts ??: If I can manage 8km/h now early in the morning with quiet see maybe once the boat is cleaned, antifuled and prop speed applied on the propeller will I get that 11km/h? If that is the case what is the point of spending 1200 bucks for a new propeller. The issue is thst propeller can be changed only when boat is out. At that point I will not know if I can get 6knots of speed.... sorry about this nonsense but I just want to know what would you guys do if you have this issue. Can someone give me his example, what is the difference in speed before and after antifuling and prop speed is applied. Can be possible that boat will eventually get to 11km/h and be more quiet?

Thank you guys for yoyr help and patience trying to understand my broken English grammar...

For 30 foot yacht it's best to passage plan on 4 knots. That's where the term 4 knot ****box came from. A Tasman 26 with a 3 blade prop might get to 6 knots in flat water and no wind. Going by the engine in this one I would think it is probably a fixed 2 blade propeller so with the average amount of slime and the odd shell I would be happy with 4 knots. Next time out and there is some distance to cover into a fresh breeze, reef the sails and motor sail. Even with just a reefed mainsail the motor will be sufficient to get you somewhere.
I would take a swim and scrape the blades on that prop before you consider changing it. Propellers are ridiculously inefficient at the best of times, especially two bladers. Half a dozen shells on my folder on a Currawong 30 dropped the speed to about 3 knots in flat water. On my SS34 with a two blade folder and a nice layer of shell and 20 hp I can nearly crack one knot at the moment in flat water!

Hi Serb.
First of all, your boat is a sailboat. The engine and propeller are added on. They are not the main driving force, so they are not as efficient as you expect.

Second, a YSE 8 is a very small engine. And old. That means the engine will probably not be producing full power anymore.

Next, I have a 25 footer with a good YSE 12 and a two bladed prop. I think your boat has had a two blade prop since new. That was what the designers chose. Even with a coat of PopSpeed or something like that , the propeller will foul up much faster than you expect and as others have said even a couple of small barnacles will make a big difference. A new 3 blade propeller will also foul quickly.

You mention vibration.
Welcome to the world of a YSE engine. These engines are the worst in the world for vibration and you will never get rid of that.


The difference between motoring in calm water and rough water, motoring into the tide and against the tide is great.
The difference between a clean hull and propeller and a slightly dirty hull and prop is great.

So, you have a sailboat with a small old engine and a dirty hull and prop. That means your boat will be slower that its top speed, but it also means your top speed (in knots or kilo/hour ) will be lower that you expect.

Don't buy a new 3 blade prop. Control your fear of sharks, dive in and clean the prop with a scraper an a scouring pad and go sailing.

PS. You mention that the engine is noisy. I wear earplugs if I have to motor more than an hour or so.

gary

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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.

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FabulousPhill said..

The answer is a clean propeller and clean hull. Then look at the number of blades and the diameter.

+1. Clean it up, first. Its way cheaper than replacing the engine and prop. I'm guessing $15K to $20K, when you allow for all the stuff you don't know about yet. That's new engine (say $9K), new prop (say $3K), new shaft (say $0.5K, because Murphy dictates that the taper for the new prop will not fit the old shaft), new electric controls, new throttle controls, adjustments to the engine beds, stuffing around re-routing the water lines, fuel lines, exhaust pipes, wiring, labour and possible slipping (because Murphy will demand that you replace the old sea-cocks, too).

I've started down the road of reconditioning my engine, and found some horrible stuff when I took the old engine out. I'm currently thinking about what to do with the engine beds, but waiting on a diagnosis on my old engine. Best outcome will be a reconditioned 8HP (or 10HP - its ambiguous) single-cylinder Bukh, which is just fine for pushing the boat in and out of the harbour, and some pedestrian motor-sailing in my 28ft Cavalier. The replacement of the broken bearing bracket might reduce the noise, too.

Serb, when you say the engine is screaming, what does the tacho read (if you have one)? If it is running up to something like max revs even with a fouled prop, that together with your observation that the prop is "tiny" could mean you have the wrong prop. A correctly sized prop if fouled badly enough to halve the motoring speed would probably load the engine such that it wouldn't rev all the way, but start smoking badly when pushed hard. My hunch is that you're up for a new prop. Regarding tapers, if the prop has a recognizable spec number on it, the supplier (if still in business) should have a record of the details and be able to supply a new one with matching taper. I did this with my new prop from Austral a few years ago and it fitted the oddball shaft taper perfectly. Some clown had fitted a ski-boat prop to my Compass 28! I hope he's languishing in the special place in hell reserved for previous owners.

Your first post seems to suggest the engine is a 1GM10. If so, its rated max output is 9hp at 3600rpm.

Good luck with it!

Graeme

Hi all I don't have revs meter, I just came back cleaned the hull as much I could, prop too. It was a lot of moss like stuff and some black ink came of the boat. I could not do much about propeller. When for a quick spin and reached 9km/h. I feel once the hull is cleand and propeller psibted with that speed prop the boat could easily reach 12km/h and that is the goal. If I am loosing 30% that 9+2.7 is around 12km/h of 6knots. That is the max hull speed.

Anyway I am having a yanmar mechanic in a week time and he will hopefully know if propeller should be replaced or we will be ok just with antifuling and speed prop. I have removed green stuff like a moss and some alge (looks like a seaweed). Black ink was going around while I was removing the moss and alge from the hull. Maybe an old copper oxide. Excuse my chemical therms. Again to reach 6km/h you can not almost hear the engine but after to push till 8 the noise is tripple. If boat could just continue to increase the speed it would be,cool to cruise at 10km/h on just just 3/4 throttle.

Like this reaching 9km/h at full open throttle just doesn't feel right. I feel engine will break soon. I am not happy at all.

If I can describe turns buy noice I would say :
1000 turns = 3 km/h
2000 turns = 6 km/h
3200 turns = 7km/h (if wind on my back 8 or even 9 is strong wind)

If strong wind against me 5 km/h if extremely strong wind that 3km/h....hard to control boat under 2km/h) feels like Keel and steering are not working)

Now why at 2000 tunrs boat goes 6km/h and with with 60% increase it gains only an extra 1km/h of 2 depending on wind?... it just doesn't make sense.
Is 5his sign of a dirty hull or it is really an effect of a small propeller. Today I cleaned it and it has 3 blades and each blade is smaller than my palm. It js really smal propeller and I have small hands. I think that each blad is around 11cm.

Any options and thoughs are appropriate.

Hi all I don't have revs meter, I just came back cleaned the hull as much I could, prop too. It was a lot of moss like stuff and some black ink came of the boat. I could not do much about propeller. When for a quick spin and reached 9km/h. I feel once the hull is cleand and propeller psibted with that speed prop the boat could easily reach 12km/h and that is the goal. If I am loosing 30% that 9+2.7 is around 12km/h of 6knots. That is the max hull speed.

Anyway I am having a yanmar mechanic in a week time and he will hopefully know if propeller should be replaced or we will be ok just with antifuling and speed prop. I have removed green stuff like a moss and some alge (looks like a seaweed). Black ink was going around while I was removing the moss and alge from the hull. Maybe an old copper oxide. Excuse my chemical therms. Again to reach 6km/h you can not almost hear the engine but after to push till 8 the noise is tripple. If boat could just continue to increase the speed it would be,cool to cruise at 10km/h on just just 3/4 throttle.

Like this reaching 9km/h at full open throttle just doesn't feel right. I feel engine will break soon. I am not happy at all.

If I can describe turns buy noice I would say :
1000 turns = 3 km/h
2000 turns = 6 km/h
3200 turns = 7km/h (if wind on my back 8 or even 9 is strong wind)

If strong wind against me 5 km/h if extremely strong wind that 3km/h....hard to control boat under 2km/h) feels like Keel and steering are not working)

Now why at 2000 tunrs boat goes 6km/h and with with 60% increase it gains only an extra 1km/h of 2 depending on wind?... it just doesn't make sense.
Is 5his sign of a dirty hull or it is really an effect of a small propeller. Today I cleaned it and it has 3 blades and each blade is smaller than my palm. It js really smal propeller and I have small hands. I think that each blad is around 11cm.

Any options and thoughs are appropriate.

Firstly when talking boat speed use knots and not Km/hr. From you description of the slime and moss on the bottom and propeller, I am very surprised that you even achieved 3 knots. Get the boat slipped and antifouled and make sure the prop is spotless, then see if you need to make any further changes. With only 8hp you will need to keep everything in perfect condition if you want to achieve 6 knots, for example I have a diver wash my boats bottom and prop every 4 weeks just to insure I get maximum hull speed and I have 110hp. In reality you should have a least a 15hp motor if you want to push any kind of sea or wind, especially if you have any fouling on the bottom or prop. There is a lot of good advice in the above comments and the common theme seems to be, get everything clean.

Understood. Thanks. It looks like I will be cleaning my hull every month ....

.................and if you can get the prop nice and clean in the water, look for those identification numbers stamped into it. If you can get these you may be able to confirm its suitability or not, and make the decision regarding a new prop before you slip. Then you can have the new one ready to fit, saving you a few days in the yard.

Indeed get the hull and prop properly clean in the water then you will be able to gauge the performance, but in reality it's a displacement hull designed to be sailed with a small engine for manoeuvring in and out of the berth

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woko said..
Indeed get the hull and prop properly clean in the water then you will be able to gauge the performance

+1, again. $15000 for a new engine vs $150 for a diver to scrub the hull and clean the prop. Please think about those extra zeroes.

Diver has cleaned the hull 3 months a go. I am so disappointed that this forum doesn't allow me to post the picture of the prop.....

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Serb1980 said..
Diver has cleaned the hull 3 months a go. I am so disappointed that this forum doesn't allow me to post the picture of the prop.....

Should be able to post pictures now. I think you have to have about 5 posts before you can usually.

As a guide to hull cleaning I try and have a bi annual slipping program, this means regular prop cleaning in the second half of the second year, if I was to leave it for 3 months the vessel would be inoperable ! If I don't use it for 3 weeks it would need a scrub. And some places are renowned for growth and require weekly cleaning. The more time you spend in the water the less terror will be experienced

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Serb1980 said..
Diver has cleaned the hull 3 months a go. I am so disappointed that this forum doesn't allow me to post the picture of the prop.....

Please don't be disappointed with the forum for the restrictions.


It may seem a slight inconvenience to you but it's saves a lot of pain from "scammers" spreading their crap.

Good things will come in time for you

Was responding to Woko's post last sentence not Craig's post which is a given.

Good plan. Not sure about the last sentence............see here bull shark movement in the harbour 8 years ago.

www.viz.org.au/bull-sharks-in-the-harbor



There are numerous more recent web links of harbour shark movements.

I have dived and scraped/scrubbed yacht hulls in the Gladesville area since the early 80s to around 2018 but won't do it anymore without a Shark Shield which have purchased............the research and product validation testing seems to be good.........but the sharks haven't read that............

spearfishing.com.au/collections/shark-shield/products/shark-shield-freedom-7c

Just saying. Experienced sailors on learning of my exploits have commented variously..........one saying that no-one has been taken by a shark when doing such hull cleaning very close to the hull. Another advising me "that's bull shark alley..." Would trust that hull cleaners doing this work as a living have some sort of shield - there are more of these shark deterrents on the market now.

Just to clarify some text previously, 1.34 is not the block coefficient - see here what it is; block coefficients and prismatic coefficients are similar and both are well less than 1.

oceansailormagazine.com/understanding-yacht-design-part-two/

www.dixdesign.com/coefficients.htm

Propeller pitch - as per original post.......

...." if I increase the pitch boat will go faster...."

This is not correct for a displacement yacht hull design like the T26 where hull speed around 6kts is the goal and keeping close to this into the waves and wind is the plan.............increasing pitch will result in the prop beating the water and cavitating or ventilating and totally loosing thrust............good article here albeit power boats..............

powerboatmagazine.co.nz/understanding-propellers/

This is why Tohatsu do their Sail Pro range - low pitch, high blade area propellers and maybe a different gearbox ratio so the prop spins slower.

www.tohatsu.com.au/content/mfs6csul-sail-pro

Have had similar comments about sharks and the local shark fishos have success in areas very close to places I clean my boat, the difference is at least what I tell myself is the set lines they employ lay on the bottom with a tasty morsel attached and the action happens at night, where as I on the other hand work near the surface with the sun high over head and have my fingers crossed

Yeah I won't clean on moorings for anyone anymore. Always at a dock in shallows now.

Finally photo.....this is a photo of the propeller. It was taken a year a go during antifuling. Yesterday took the boat for a spin. 4 knots Max. Something is not right. Hull is not that dirty. Next week a mechanic will jump on board to see what is going on. I think he will measure the revs and try to improve the speed once the boat is out on 1st December for antifuling.
It would be so cool to reach the speed of 6 knots.....if needed when wind is quite or none at all.. please guys can someone comment it this propeller is 15x12 and is this is left of right... A worker at Austral told me that with my engine yse8 and propeller 15x12 3 blade boat should get 6.5knots..
Any thoughts? Buy the way a propeller is around 1200 bucks at Austral.
Thanks