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

I agree theres going to be a risk in buying a secondhand engine but thats the risk of the
tight finances. Surely cutting a bloody great hole in the bottom of a boat carries its
own risk? Has it been done to a Centaur before? Or any yacht of a similar vintage.
What if it dosent work and it bends like a banana? IANAMA (I Am Not A Marine Architect)
but I dont think the original designer had a modification like this in mind when the hull
was designed.

If the engine is a duff one you have wasted £1500 on a broken engine; you could always
relist it on ebay. If you cut the hole in the hull it could be the end of the boat all together;
you'll never resell it.

And the Centaur-massif crowd will never forgive you :-)

jono
 
Twister_Ken said:
Whether or not it 'works' Dylan will end up with the noisiest Centaur in captivity, the one that creates the most turbulence when sailing, the one with the least amount of room in the cockpit, and the one with the most easily nickable engine.
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entirely correct on all counts


on the other hand it will not be one of those Centaurs moldering in a yard with a dead engine

I will have the full standing headroom and sea keeping qualities of a great boat (assuming I can design a well that does not allow the sea to come surging in)

my cockpit will be bigger than the one I have now

I already sail with an outboard stuck in the water and I am not too concerned about the extra turbulence. I have done tests on Katie L and I reckon it is a maximum of half a knot

I hate the noise of an outboard (but I am also not that keen on the noise of an inboard)

when motoring for any distance put the tiller pilot on and retreat to the bows

Dylan
 
I would have thought that the cheapest and easiest option for an outboard powered Centaur is to get an ultra-long one and stick it on the back at a level such that the prop is well below the water surface. This is the arrangement on my boat. The prop has never come out of the water and the engine doesn't seem to mind the occasional pooping. I have heard it said that the extra depth will create back pressure on the exhaust to some detrimental effect or make starting harder. I suspect that this is a throwback from 2-stroke engines as I have never had any problem. An electric start and remote control for another £200 will solve any inaccessability problems. Then if it doesn't work, you don't have a too badly butchered boat.
 
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The above seems the best compromise, stick it on the back for a season and see how it goes, but I fully understand you wanting to get the prop underneath and I am considering doing the same thing although it will be two holes in my case and I already have the engines.
 
Croak said:
The above seems the best compromise, stick it on the back for a season and see how it goes, but I fully understand you wanting to get the prop underneath and I am considering doing the same thing although it will be two holes in my case and I already have the engines.
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I did email David Pugh of PBO about the idea

Hi Dylan,

Why not – sounds like it should have some good practical stuff in it, even if you're not receiving wholehearted support from the forum!

Can you make sure you add in some copy about why you wanted to do it, especially vs a new or second-hand inboard?

Cheers,
David.

so I reckon it has got to be good for two pages

that is the first £200 towards the costs of the plan

all I need is the remaining £4,800

D
 
I'd be worried about the structural integrity if you cut a well in the hull. Surely the centreline of the hull will have additional strength - thicker layup, if not a structural element? There is certainly a substantial thickening housing the existing propellor shaft, according to the diagrams posted. I'd be seriously concerned that I'd end up with a hull unable to take the bending stresses imposed by the rigging (the mast pushes down, the stays, especially the backstay in this case, pull up), or the bending stresses imposed by waves passing under the hull.

By cutting a hole for a well, I am sure you'd compromise the girder strength of the hull so it was less able to take the stresses imposed by the rig, and also the bending stresses imposed by waves. There would also be issues with stress concentration at the corners of the well. I wouldn't consider doing it without a proper structural analysis by a qualified marine architect. Marine architects aren't cheap, and this kind of analysis would be a costly business - but without it you have a hull whose strength is unknown, and potentially seriously compromised.

It might work fine for a while, but one day when you're sailing hard in a bit of a sea, you could find you have two boats instead of one!
 
AntarcticPilot said:
I'd be worried about the structural integrity if you cut a well in the hull. Surely the centreline of the hull will have additional strength - thicker layup, if not a structural element? There is certainly a substantial thickening housing the existing propellor shaft, according to the diagrams posted. I'd be seriously concerned that I'd end up with a hull unable to take the bending stresses imposed by the rigging (the mast pushes down, the stays, especially the backstay in this case, pull up), or the bending stresses imposed by waves passing under the hull.

By cutting a hole for a well, I am sure you'd compromise the girder strength of the hull so it was less able to take the stresses imposed by the rig, and also the bending stresses imposed by waves. There would also be issues with stress concentration at the corners of the well. I wouldn't consider doing it without a proper structural analysis by a qualified marine architect. Marine architects aren't cheap, and this kind of analysis would be a costly business - but without it you have a hull whose strength is unknown, and potentially seriously compromised.

It might work fine for a while, but one day when you're sailing hard in a bit of a sea, you could find you have two boats instead of one!
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it looks as though the hole would be aft of the prop shaft housing - so that bit of structure can remain intact

I think that the right strengthening around the hole if properly bonded to the hull would do a pretty good of transferring the forces

of course I am not a marine architect....but maybe one will be along in a minute

D
 
I love my diesel inny, works great and , let's face it , the boat was designed for it. Bunging an outy in a well will remove the structural integrity of the boat and may make her uninsurable except for third party cover ( The difference between 3rd party and fully comp on our boat is about £45 !) Also, with an outy you will have the added joy of an undersize alternator failing dismally to keep lights, nav instruments and leisure batteries topped off.
Bite the bullet and get the old engine rebuilt or go for a new inboard engine and enjoy being one of the Centaur aficionados who populate the forum pages !

Good luck whatever you choose to do :)

GOG
 
GrumpyOldGit said:
I love my diesel inny, works great and , let's face it , the boat was designed for it. Bunging an outy in a well will remove the structural integrity of the boat and may make her uninsurable except for third party cover ( The difference between 3rd party and fully comp on our boat is about £45 !) Also, with an outy you will have the added joy of an undersize alternator failing dismally to keep lights, nav instruments and leisure batteries topped off.
Bite the bullet and get the old engine rebuilt or go for a new inboard engine and enjoy being one of the Centaur aficionados who populate the forum pages !

Good luck whatever you choose to do :)

GOG
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lekkie not really a problem anymore

my Tohatsu kicks out enough power to keep my batteries charged and the lights on

I have around 20 camera batteries to charge off the 12 volts, plus the laptop

I do not have any solar or win generators on Katie L

I do have a spare battery that I keep topped up - but have never needed it

and there is now no need to have a battery just for the engine...if the domestic gets run down then you have a hand starting engine anyway

as for wrecking the structural strength....

that is obviously a concern

but

is a Centaur so lightly built that cutting a small hole would cause the whole thing to fall apart?

I am sure that the right shaped box around the hole will allow all the forces to be transferred

maybe some-one who knows will be along soon

D
 
dylanwinter said:
and man you get a good financial kicking when you take one of those into a marina
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Not in the UK you don't. In €land you do where they charge for length x beam, but in the UK I have never been charged extra for my 9m x 6m. I sometimes get a berth at the far end of the furthest pontoon somewhere past the back of beyond where the seagulls lurk, but never had to pay more.
 
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http://www.socasailboats.com/CRO_System/body_cro_system.html

How about a DIY version of this one?
 
Phil Bolger had a point I reckon when he wrote how he disliked outboard wells "because they take up even more space than an inboard engine". OTOH there's the weight penalty and cost associated with diesels. You *could* of course fit one of these cheap Chinese "MPower" engines @2-3K but then again that would mean a lot of work for an inferior quality diesel lump.
 
dylanwinter said:
it looks as though the hole would be aft of the prop shaft housing - so that bit of structure can remain intact
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Surely everything about the project needs to be designed to ensure that the well is just aft of the shaft housing / skeggy bit - as you say, putting the new prop in the same place as the old. Cutting through that central spine would be madness, whereas hiding the outboard leg behind it should actually minimise the drag.

dylanwinter said:
I think that the right strengthening around the hole if properly bonded to the hull would do a pretty good of transferring the forces
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Have to say, I'm with you on this bit. Assuming the job's done right, my gut feeling is that an outboard-sized hole in that location is not going to be a serious problem for a 70s-style tough-as-old-boots Westerly hull. If anything was going to fail my money would be on the well tube separating from the hull, rather than the hull itself failing. But it should be perfectly possible to make that joint strong enough; it's not dissimilar from the process of fitting a saildrive.

Pete
 
dylanwinter said:
wow that is clever

of course outboard wells in big boats don't work so it will never catch on

D
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I said I wasn't going to play anymore but I can't sit this one out.

Melges vs centaur. interesting comparison.

As I said in an earlier post in a lightweight sportsboat (like a j/80 or a melges) I would have an outboard. The J/80 I have sailed on has a 3.3 tohatsu. I dont see the need for a well at all? transom is fine. The outboard gets the boat off the pontoon and through the lock. the sails go up. the outboard comes off and goes in a locker. its no longer needed. with the weight and the strength of the large crew that boat doesnt need an engine. in some ways, to a lesser degree seajets anderson is much the same. It will perform well enough under sail alone that the outboard is fine.

Im not slating centaurs, they sail well for what they are. But find yourself on a lee shore in a nasty short chop or caught wind against tide and you are going to need the motor to get you out of the poo (particularly if short handed) and why the hell not - if youre not racing I really dont see the catch.
 
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