Tohatsu MFS9.8A3 UL 9.8HP 4STR UL (£2,141.41p) in westerly centaur with dead engine

[Tranona]

it is a high thrust long shaft 9.8hp optimised for displacement boats

it will deliver 9.8 hp at the prop

the Centaur was designed for a new 10 hp diesel measured at the engine

as I understand it I will delivering slightly more thrust than LG designed the boat for

D

You are tying yourself up in knots about what makes an effective auxilliary. Get it straight - it is the propeller that moves the boat not the engine. The concept you have constructed quoting HP at the prop as being better than HP at the engine is just nonsense. Propellers do not produce HP, but thrust determined by their size, pitch and speed. So that is what you start with and then work back to get the HP you need to turn it at sufficient speed to move the boat.

The boat was NOT designed for a 10hp engine. The original was 13hp, and even in those days when speed expectations were lower than today it was underpowered (that is there was not enough power to turn the ideal prop) and would barely reach hull speed in flat water - but that was all that was available at the time. The 23hp engine was fitted to later models because that was the next size up. If you look at most of the re-engine jobs you will find the 18-20hp range is the most commonly fitted because that is the appropriate size.

So, you are deluding yourself thinking that the outboard will be a satisfactory auxiliary for when you get to the more demanding part of your journey.

Equally your long diatribe about the inadequacy of small diesels is so far from reality that it is almost impossible to believe you are serious. I know your view is based on your experience with your ancient Volvo, but that is a bit like saying I won't have a Fiesta because I once had a Popular (which I did and remember the wipers that did not work, the need for a decoke every 10000 miles etc.). Modern diesels are as far removed from your old nail as a Fiesta is from a Popular.

You want a reliable boat and engine for your journey. Why are you thinking about a knackered boat and an inadequate engine when you can buy a complete boat for similar money which will do everything you want - and then sell it afterwards, probably for more money as the "been there done it" ex KTL star.

 

[JumbleDuck]

I am astonished at the reaction of some blokes who seem really fixated on dissing an attempt by a fellow sailor to get a good sea boat with full standing headroom and a reliable engine.

I think you are seeing some people getting very, very defensive about their own choices of boat.

 

[dylanwinter]

You are tying yourself up in knots about what makes an effective auxilliary. Get it straight - it is the propeller that moves the boat not the engine. The concept you have constructed quoting HP at the prop as being better than HP at the engine is just nonsense. Propellers do not produce HP, but thrust determined by their size, pitch and speed. So that is what you start with and then work back to get the HP you need to turn it at sufficient speed to move the boat.

The boat was NOT designed for a 10hp engine. The original was 13hp, and even in those days when speed expectations were lower than today it was underpowered (that is there was not enough power to turn the ideal prop) and would barely reach hull speed in flat water - but that was all that was available at the time. The 23hp engine was fitted to later models because that was the next size up. If you look at most of the re-engine jobs you will find the 18-20hp range is the most commonly fitted because that is the appropriate size.

So, you are deluding yourself thinking that the outboard will be a satisfactory auxiliary for when you get to the more demanding part of your journey.

Equally your long diatribe about the inadequacy of small diesels is so far from reality that it is almost impossible to believe you are serious. I know your view is based on your experience with your ancient Volvo, but that is a bit like saying I won't have a Fiesta because I once had a Popular (which I did and remember the wipers that did not work, the need for a decoke every 10000 miles etc.). Modern diesels are as far removed from your old nail as a Fiesta is from a Popular.

You want a reliable boat and engine for your journey. Why are you thinking about a knackered boat and an inadequate engine when you can buy a complete boat for similar money which will do everything you want - and then sell it afterwards, probably for more money as the "been there done it" ex KTL star.

I apologise

 

[jono_howlett]

Tranona I think that's a bit below the belt. Despite Dylan's affable style he is a determined character; I would have probably given up on the same mamouth trip given the trials and tribulations so far most of which have, to be fair revolved around the inboard engine. I think Dylan has made his mind up and is here for advice so chaps, let's pull together and see if this project can be pulled off. For the record I think the inboard is the way to go but let see what happens. Dylan, I expect lots of videos of you covered in resin, fibreglass powder etc!

Jono

 

[JumbleDuck]

Tranona I think that's a bit below the belt. Despite Dylan's affable style he is a determined character; I would have probably given up on the same mamouth trip given the trials and tribulations so far most of which have, to be fair revolved around the inboard engine. I think Dylan has made his mind up and is here for advice so chaps, let's pull together and see if this project can be pulled off. For the record I think the inboard is the way to go but let see what happens. Dylan, I expect lots of videos of you covered in resin, fibreglass powder etc!

Perhaps the redundant engine bay could be converted into a titchy little double cabin to keep the AWB boys happy?

 

[Tranona]

I apologise

Apology accepted (but I not sure what for).

Just to illustrate how far you are away from reality, a few hard facts.

Your proposed outboard has just under 10 hp at between 5-6000 rpm and a reduction ratio of 2.08 and the high thrust prop is an 8.7*5. Calculations show that the ideal prop for that hp to push your 3 ton boat (although it will be nearer 4 with all your gear) is a 9.4*6.6 - that is substantially "bigger" than the prop you will actually get. Even then the predicted maximum speed is only 5.4 knots - more than a knot below the maximum displacement speed. With the smaller prop you will not even reach that, probably less than 5 knots.

On the other hand, if you have the sort of engine recommended for the boat such as a Beta 20hp with a 2:1 box you will swing a 12.5*9.3 (in practice a 13*9) and easily achieve the displacement speed of 6.46 knots - more than 20% faster than the outboard. Remember these speeds are in flat calm and in any kind of sea or headwind the outboard will lose what little speed it has very quickly.

This is a different world from the boats you have been using in the past and your current boat, where an outboard is a perfectly acceptable form of propulsion. In part it was the development of reliable small diesels that made boats like the Centaur what they are and why they are capable of undertaking voyages such as you are planning.

So, my turn to apologise for introducing some harsh reality into the debate.

 

[Twister_Ken]

Tranona

...until you're blue in the face!

DW has decided than any diesel is the spawn of the devil, while the sun shines brightly from the a*se of an outboard.

You, me and a team of wild horses ain't gonna convince him otherwise.

Sit back and enjoy the show, which is scheduled for 2019.

 

[dylanwinter]

Apology accepted (but I not sure what for).

Just to illustrate how far you are away from reality, a few hard facts.

Your proposed outboard has just under 10 hp at between 5-6000 rpm and a reduction ratio of 2.08 and the high thrust prop is an 8.7*5. Calculations show that the ideal prop for that hp to push your 3 ton boat (although it will be nearer 4 with all your gear) is a 9.4*6.6 - that is substantially "bigger" than the prop you will actually get. Even then the predicted maximum speed is only 5.4 knots - more than a knot below the maximum displacement speed. With the smaller prop you will not even reach that, probably less than 5 knots.

On the other hand, if you have the sort of engine recommended for the boat such as a Beta 20hp with a 2:1 box you will swing a 12.5*9.3 (in practice a 13*9) and easily achieve the displacement speed of 6.46 knots - more than 20% faster than the outboard. Remember these speeds are in flat calm and in any kind of sea or headwind the outboard will lose what little speed it has very quickly.

This is a different world from the boats you have been using in the past and your current boat, where an outboard is a perfectly acceptable form of propulsion. In part it was the development of reliable small diesels that made boats like the Centaur what they are and why they are capable of undertaking voyages such as you are planning.

So, my turn to apologise for introducing some harsh reality into the debate.

sorry

 

[dylanwinter]

Tranona

...until you're blue in the face!

DW has decided than any diesel is the spawn of the devil, while the sun shines brightly from the a*se of an outboard.

You, me and a team of wild horses ain't gonna convince him otherwise.

Sit back and enjoy the show, which is scheduled for 2019.

sorry

 

[AngusMcDoon]

Just to illustrate how far you are away from reality, a few hard facts...

When the inboard engine failed on my previous 33' boat (an X99, 3 tonnes) on a completely calm day I returned 13 miles to port being pushed by my 2hp Honda outboard attached to the inflatable. At about half throttle we were doing just over 4 knots. Does this agree with your calculations?

 

[dylanwinter]

When the inboard engine failed on my previous 33' boat (an X99, 3 tonnes) on a completely calm day I returned 13 miles to port being pushed by my 2hp Honda outboard attached to the inflatable. At about half throttle we were doing just over 4 knots. Does this agree with your calculations?

I did the same with a 30 ton butty canal boat laden with soap and candles

2hp seagull on an inflatable

we got her going at a pretty good walking pace

no wind, no current, no waves of course

 

[Tranona]

When the inboard engine failed on my previous 33' boat (an X99, 3 tonnes) on a completely calm day I returned 13 miles to port being pushed by my 2hp Honda outboard attached to the inflatable. At about half throttle we were doing just over 4 knots. Does this agree with your calculations?

Yes. On a flat calm you can move a surprising amount of boat with small hp. see the article in YM two months ago. My 6 ton + 37 footer uses about 9 hp to move it at 5.5 knots.

However, once you want to go above those sorts of speeds the power requirements rise rapidly. Again on my boat the hp requirement nearly doubles to get from 5.5 to 6.5 - you can tell this by the fuel consumption increase.

There is a big difference between moving a boat at low speeds in a flat calm and having a usable auxiliary that will make most use out of the displacement speed potential of the boat.

If you go back a post or two of mine you will see my emphasis on the propeller as the important factor in the calculation. You simply cannot get a big enough propeller on the outboard to achieve displacement speed. If you could bring the shaft speed down to around 1500 - that is a reduction ratio of 3.5:1 instead of the current 2:1 then you could swing a 12 or 13" prop which would improve the speed, and more particularly reduce the impact of adverse conditions on speed. However that is physically impossible as there is not enough room in the transmission.

This is the fundamental difference between outboards designed for light craft where you can run small diameter props fast to get the speed and large slow turning props that are used on inboards for heavy displacement boats. The so called high thrust outboards are an attempt to deal with the issue, but they are a compromise and sub optimal for the job.

 

[AngusMcDoon]

I did the same with a 30 ton butty canal boat laden with sooap and candles

2hp seagull on an inflatable

we got her going at a pretty good walking pace

no wind, no current, no waves of course

Rather than replacing your current boat with its brand new engine why don't you bring it back by road to your starting point and head west? There would be years worth of coast to cover before the same problem rose again.

 

[bendyone]

Loaded narrow boat only needs 1 horsepower.

 

[Tam Lin]

Rather than replacing your current boat with its brand new engine why don't you bring it back by road to your starting point and head west? There would be years worth of coast to cover before the same problem rose again.

Keep turning right?

 

[fergie_mac66]

On the other hand, 10hp in a boat of that size wouldn't have raised an eyebrow in the 70s or 80s. It's only received wisdom now that every sailing boat must have a ruddy great engine in case the wind outside the marina isn't F3 on the beam.

too true,
Eric and Susan Hiscock went round the world in wanderer III (30foot heavy wood built) with a 4hp engine with an off center propshaft, I believe

 

[Simonpk]

Dylan, go for it. I love these, what some people call, crazy ideas. I reckon there was loads of armchair critics who though Ken Wallis was "Barking" when he strapped helicopter blades onto little more than a lawn mower engine.

You don't wont to grow old sitting in your rocking chair pondering whether it would have worked or not. Try it, if it doesn't work at least you tried, if it does, Result!. They can't hang you for it.

I don't know if anyones mentioned the tiller arrangement in a Centaur tho. This might need a further mod as the tiller attaches at cockpit floor level and sweeps across the cockpit at low level until it curves up.

View attachment 36282

 

[dylanwinter]

thanks

Dylan, go for it. I love these, what some people call, crazy ideas. I reckon there was loads of armchair critics who though Ken Wallis was "Barking" when he strapped helicopter blades onto little more than a lawn mower engine.

You don't wont to grow old sitting in your rocking chair pondering whether it would have worked or not. Try it, if it doesn't work at least you tried, if it does, Result!. They can't hang you for it.

I don't know if anyones mentioned the tiller arrangement in a Centaur tho. This might need a further mod as the tiller attaches at cockpit floor level and sweeps across the cockpit at low level until it curves up.

View attachment 36282

I really do not want to touch the tiller

although I assume just laminating up a new one with more extreme curve should be possible and fairly simple

I love a tiller extention anyway - so that I can stand on the cockpit seat to steer/film/get away from the sound of the engine/reach control lines onthe cabin top

D

 

[Bru]

I did the same with a 30 ton butty canal boat laden with soap and candles

2hp seagull on an inflatable

we got her going at a pretty good walking pace

no wind, no current, no waves of course

No seagull required, just rope up my brother! (He wasn't referred to as "Neddy" around the working boats for nothing!)

It doesn't take much power to keep a narrowboat moving once you've got it started

Unfortunately, coastal waters are sadly lacking in towpaths otherwise I'd offer his services which would undoubtedly be more effective than an outboard in a Centaur!

OK, jesting aside, I still think this is a dumb idea arising out of a combination of an unreasonable prejudice against the best solution based on one bad experience, sheer bloody mindedness and a characteristic determination to plough a slightly different furrow to that which convention would dictate but ...

I am increasingly persuaded that the good Mr Winter is cognisant of all the drawbacks and pitfalls and has actually thought this thing through quite thoroughly

I still think there's a fly in the ointment though, even if one accepts that the outboard well will work to an acceptable level of performance for the intended purpose (i.e. it will get the boat in and out of port and push it along passably well in flat conditions).

The spoiler, already alluded to but not I fear taken fully on board (aha ha ha) is that a Centaur with a knackered engine is also probably burdened with knackered sails, knackered rigging (running and standing) and a slew of other ultimately costly to resolve problems

So this boat that is going to be sailed everywhere and therefore isn't going to need anything more than an auxiliary engine to get it on and off the dock isn't going to be much cop under sail either.

And the cost of re-rigging, new sails and all the other bits and bobs of sorting out that this mythical £2k Centaur is realistically going to need is going to once again add up to as much or more than it would cost to by a half decent one in the first place

I await the cunning swerve that will no doubt avoid this issue with eager anticipation!

 

[dylanwinter]

No seagull required, just rope up my brother! (He wasn't referred to as "Neddy" around the working boats for nothing!)

It doesn't take much power to keep a narrowboat moving once you've got it started

Unfortunately, coastal waters are sadly lacking in towpaths otherwise I'd offer his services which would undoubtedly be more effective than an outboard in a Centaur!

OK, jesting aside, I still think this is a dumb idea arising out of a combination of an unreasonable prejudice against the best solution based on one bad experience, sheer bloody mindedness and a characteristic determination to plough a slightly different furrow to that which convention would dictate but ...

I am increasingly persuaded that the good Mr Winter is cognisant of all the drawbacks and pitfalls and has actually thought this thing through quite thoroughly

I still think there's a fly in the ointment though, even if one accepts that the outboard well will work to an acceptable level of performance for the intended purpose (i.e. it will get the boat in and out of port and push it along passably well in flat conditions).

The spoiler, already alluded to but not I fear taken fully on board (aha ha ha) is that a Centaur with a knackered engine is also probably burdened with knackered sails, knackered rigging (running and standing) and a slew of other ultimately costly to resolve problems

So this boat that is going to be sailed everywhere and therefore isn't going to need anything more than an auxiliary engine to get it on and off the dock isn't going to be much cop under sail either.

And the cost of re-rigging, new sails and all the other bits and bobs of sorting out that this mythical £2k Centaur is realistically going to need is going to once again add up to as much or more than it would cost to by a half decent one in the first place

I await the cunning swerve that will no doubt avoid this issue with eager anticipation!

this project depends of getting the right candidate boat at the right place at the right price

I am after the sort of boat most other people will walk past tutting to themselves

grime and a knackered interior.... no worries

I want one where the keels have been fixed, I want the rudder tube to be in good nick, I want decent standing rigging and dry stored sails, and a dry interior

nothing else is mission critical

knackered standing rigging is my main concern

I do not want the mast to fall down

knackered sails I can live with

this is a Centaur, not the World's greatest sailing vessel - but better than the slug which I sailed for five years - five years lads

what is the difference between a boat with knackered sails and one with brilliant ones - half a knot perhaps upwind

down wind I do not think it makes a jot of difference

there are lots of old Centaur sails available

Running rigging I can replace as and when it breaks

people have mentioned headlining, electrics, plumbing

none of these are mission critical

I went to a state run boarding school... I sail in the winter in a boat with no upholstery - just a lilo and a sleeping bag


I cook on a meths stove let in to a wooden box

no sink

even a functioning bog is not important



Running this around the forum has helped massively as it has thrown up lots of snags and forced me to confront my devils

and obviously deeply angered some people to the point of using language they would never use in the real world to a fellow stranger

the inside of their heads must be a weird place indeed

all I can say is that Saving a Centaur from a slow moldering death in the corner of a yard is a bit more useful than blowing a boat to smithereens

If the outboard well idea fails then a lot of people will be more than happy to say "I told you so" from the comfort of their own keyboards


On the other hand there are a few blokes - including those at Tohatsu, Wessex and PBO who think I have a chance of pulling it off.

I have very few worries about the power of the engine - the racing boys use wells on some pretty big yachts

ploughing into a head sea is not something I do very often - bashing along with a genoa furled out and the outboard on a third revs is much more common

I have had some great feedback from Sailing Anarchy - they do some pretty long delivery trips and move their boats in and out of marinas under all sorts of conditions

10 hp in a four tonne 30 footer is a fairly common - easily driven hulls and six blokes on board etc etc

at the moment I have three main concerns

1/will the North Sea come back up my well?

2/Can I find the right candidate boat at the right place

3/balancing the finances