Best extra-long shaft outboard, for driving displacement hulls?

[Big-Bang1]

I have a Tohatsu 9.8 four stroke extra long shaft high thrust (four bladed prop) on my leisure 23SL, it's superb!
Easy to start, runs quietly and is So economical. I wouldn't hesitate to recommend it to others.
It's for sale a the moment, comes with a free Leisure 23SL

 

[dancrane]

The usual method is to use bollard pull - attaching the boat to a load cell fixed to the shore. Spent many happy hours doing just that on various...Seagulls compared with others of notionally higher HP. In fact the model names of the motors I was involved with (1978-81) reflected thrust in pounds - an effort to get away from the use of horsepower...Modern engines do quite a reasonable job - and are quiet, smooth, clean - and have reverse gears which few Seagulls had.

This is very interesting, thanks Mr T. So...what I'm really interested in, is whether the lower gearing and bigger, slower-turning propellor of an engine which is rated at x-horsepower, can create more bollard-pull thrust than a smaller-propped outboard rated at greater horsepower. Isn't that the whole basis of 'sail-power' outboards?

Edit: You seem to have confirmed this in your earlier post.

 

[Tranona]

Yes. Water under the bridge now, but you would be surprised how little power the old Seagull engine produced - even compared with the often optimistic claims of the then competitors for similar engines. That was one of the reasons why we emphasised thrust. The Silver Century+ and 110 models both provided more thrust than the competitors rated at 5 or 5 hp.

 

[stephen_h]

Not any more they don't. At 10hp for extra long it's Honda, Tohatsu or Selva now.

Yamaha still make a 9.9 high thrust[URL="http://www.yamahaoutboards.com/outboards/High-Thrust/overview"/URL],[/URL] but do
you mean they don't make a long shaft anymore? If not they have shot themselves in the foot since it is a popular engine!

 

[AngusMcDoon]

Yamaha still make a 9.9 high thrust, but do you mean they don't make a long shaft anymore? If not they have shot themselves in the foot since it is a popular engine!

The latter. The 9.9 high thrust is standard or long only now, not extra long any more. It's a shame as it was the best in the class, but I imagine they just didn't sell enough to justify the extra model.

 

[fergie_mac66]

The latter. The 9.9 high thrust is standard or long only now, not extra long any more. It's a shame as it was the best in the class, but I imagine they just didn't sell enough to justify the extra model.

Its the same with other hp we have 25hp long shaft but the exlong was always a extension casting on the long shaft . The importers wont do the extensions but it is avail in USA.It really is very easy to fit . I did it in the back of an estate car in a car park . Its a 5inch casting, 4 long studs with water-pipe, gear-change and drive shaft extensions

 

[onesea]

As best as I can work out thrust in water is funny thing... Small high reving good for speed but for bollard pull you want large and slow....

I could be wrong but if you could have everything... Accelerating a big boat with low horse power..

You would want:
1: large slow turning low pitch prop..
2: Changing to faster turning less pitch prop (not to much to cause cavitation that's your enemy),
3: As speed increases you continue same way,

To get good thrust you need slower turning but correct pitch to match...

Most modern outboards are for small fast boats, how often do you see here "will it plane with my xxxx 2.5 horse?"

A seagul (beautiful machines they are) will get very little on the plane but that same 2.5 horse will win the tug of war with the modern engine...

Net result is to push a big boat with a modern outboard you need lots of horses as they are race horses you are buying not the cart cart horses you need....

 

[dancrane]

Thinks for a minute...

...so...the unashamedly modest horse-power of the Seagull was put to its best use as a low-geared, slow-running big-prop turner...

Wouldn't trolling outboards - or other electric motors, with their high torque at low revs - replicate the barge-pusher principle quite well?

 

[Seajet]

Dan,

I'm certain electric motors are the way to go for the high torque reasons you describe, but it will be a while yet.

When we were hoping to put the A22 back into production I was extremely keen on an electric motor, but after chatting with a chap from Torqueedo it became clear that with present ( vaguely affordable ) technology the boat must be designed around the battery as ballast, pretty much like a diesel/electric submarine - a U-Boat !

Trolling outboards are really, really low power, insufficient to push a dinghy into wind & wave, while Torqueedo jobs are spiffing but mind-numbingly expensive when one considers an extra battery pack for range & safety.

 

[lw395]

Unless we're really talking about day sailing pretty small boats, or racing boats that will store the outboard below most of the time, I don't think an ultra long shaft outboard is what I'd be looking for.
A standard shaft outboard in a well has its attractions.

The bollard pull of big props is all very well, but I don't use boats for pulling bollards.
There ought to be a better way of measuring useable spread of thrust vs speed.
You want a bit of thrust in reserve for pushing into wind or waves, but you don't want to be using too many revs at cruisng speed on flat water.
Having known a lot of Impala owners, most were convinced the 1gm diesel was the way to go if you wanted to use the boat cross channel.
Many Impalas were converted from outboards in wells.
A diesel is not cheap, but say you're going to keep the boat 5 years, it's not the biggest cost and may mean you get more out of the boat in terms of cruisng range.
Noisy damned thing that makes you want to sail instead, but is that bad?

 

[dancrane]

I'm certain electric motors are the way to go for the high torque reasons you describe, but it will be a while yet...Trolling outboards are...insufficient to push a dinghy into wind & wave, while Torqueedo jobs are spiffing but mind-numbingly expensive when one considers an extra battery pack for range & safety.

Yeah, I s'pose I knew that really. I just thought that nobody seems yet to have offered an electric motor with a really big, slow prop...although I thought I'd heard of massively heavy electric canal boats arranged on those lines; but of course battery weight is no constraint on narrow boats, and it's absolutely prohibitive in small sailboats.

...I don't think an ultra long shaft outboard is what I'd be looking for. You want thrust in reserve for pushing into wind or waves...a lot of Impala owners...were convinced the 1gm diesel was the way to go if you wanted to use the boat cross channel...A diesel is not cheap...Noisy damned thing that makes you want to sail instead, but is that bad?

Perfectly fair and sensible; and even if it wasn't it'd still make sense, if in practice it's what most owners end up preferring.

To be honest I was thinking about small catamarans, where options are often quite varied. But weight-saving seems vital in cats; I get the impression people who fit a diesel in each hull for the unarguable security, end up using them more often because the heavily-laden boat with submerged props, sails less well. Plus, inboards occupy lots of space.

Then again, many seem opposed to relying on an outboard on the bridgedeck because the prop sometimes jumps clear of the water. Hence my extra-long-shaft o/b query.

Silette retractable legs sound a good idea though they're not reputed for reliability, but how much heavier, noisier and costlier must they be, teamed up with a central diesel?

This is all just me dreaming, there's no need for any conclusion.

 

[lw395]

Catamarans are a special case, and vary a lot.
If it's not big enough for twin diesels, then twin outboards may be the right answer for in-harbour work, the kind of smallish cat I quite like would be something to only motor as a last resort.

 

[onesea]

When we were hoping to put the A22 back into production I was extremely keen on an electric motor, but after chatting with a chap from Torqueedo it became clear that with present ( vaguely affordable ) technology the boat must be designed around the battery as ballast, pretty much like a diesel/electric submarine - a U-Boat !

When I had my little 24 and even now with this boat if I could have disel electric... Modern Genset powering an electric motor even a boat the size of a A22 it could work well. Some batteries for "silent running" during berthing, Sola to top the batteries up and Genset for longer periods. The genset could also power a 240v system on the boat, hair driers microwaves etc etc... Big boats could have 2 or 3 Gensets so you have reserves.

At present the cost is just prohibitive.

The bollard pull of big props is all very well, but I don't use boats for pulling bollards.

This is true yet when you want to move a heavy boat with small engine you want push as much as speed, larger propellers can develop more push than smaller ones.

As this thread shows modern outboards are designed to move light displacement boats fast, moving heavier displacement boats relatively slowly is an after though as there is not that great a demand.

 

[dancrane]

...the kind of smallish cat I quite like would be something to only motor as a last resort.

I like performance cats too; but owners of small cruising cats often admit they're really poor to windward, especially when laden, so a lee-shore would test the auxiliary thoroughly.

The question must be whether to concede the design's inadequacies as a sailing machine and fit a hefty inboard (or 2) for security, or whether to weight-save & sail more...

...which would sound preferable, if there's a big-enough outboard with a long-enough shaft.

Modern Genset powering an electric motor...it could work well. Some batteries for "silent running" during berthing, solar to top the batteries up and Genset for longer periods. The genset could also power a 240v system on the boat, hair driers microwaves etc etc... Big boats could have 2 or 3 Gensets so you have reserves.

We share the dream!

 

[catalac08]

Tohatsu do an ultra long shaft (27") in the 15, 18 and 20 hp and maybe the 25/30 Hp too. These do not have quite as good a gear ratio as the 9.9 Yamaha but in some ways may be a better motor. My 20hp on a 3T cat cruises at 5.5 knots comfortably with a max of 7 knots. It rarely cavitates but has a rev limiter so no real problems anyway. Under power my boat seems about the same as most 32ft monohulls which by the sound of them are all diesel engined. It has 15A charging and power tilt and is also startable with the hand start if electrics are down. It uses about 0.4 gallons per hour cruising and about 1 gallon per hour at WOT.
I have never felt vulnerable through not having enough power to get out of trouble and yes small cats are not good to windward but so are many small twin keel monohulls and the cats are soooo comfortable to live on, less tiring on the skipper and crew and the ability to cook an passage that swings it for me and the poorer windward ability becomes a minor element. Also a joy to sail off the wind with no rolling downwind or at anchor. The emphasis of priorities is a very individual thing and it would be boring if we all had the same tastes!

 

[AngusMcDoon]

As this thread shows modern outboards are designed to move light displacement boats fast, moving heavier displacement boats relatively slowly is an after though as there is not that great a demand.

My Yamaha 9.9 pushes my 2.5 tonne trimaran no problem at all. I wouldn't swap it for a ratty old Seagull however big its prop and amazing its bollard pull. I get 22 Nm per gallon at 5.5 knots in calm weather whereas a nasty old 2 stroke Seagull would guzzle fuel and leave a slick in its wake wherever it went, assuming it started in the first place. My engine doesn't seem to suffer from lack of thrust because the base engine is designed for boats that motor faster. It provides ample thrust for maneuvering in winds that I would rather not be maneuvering in. 15 years old on a boat that has logged 33k miles and no problems yet. But as you say, there is not great demand, and Yam have stopped making it.

 

[dancrane]

Thanks gentlemen, that's very encouraging. I'm easily persuaded of the appeal of multihulls; but I'd have to re-wire my mind to accept deficient windward speed & pointing.

With that in mind, I'd want an engine that isn't defeated by the sort of waves a force 5 produces; the Tohatsu saildrives look worth investigating...http://www.tohatsu-uk.net/

Particularly that 9.8 with the 25" shaft.

 

[AngusMcDoon]

I'm easily persuaded of the appeal of multihulls; but I'd have to re-wire my mind to accept deficient windward speed & pointing.

Deficient pointing like this you mean? 30 degrees apparent wind angle, 21 knots apparent wind speed, 10.2 knots boat speed...

Surprisingly, not all multihulls are the same, although because a Heavenly Twins is not so hot to windward that means, according to forum wisdom, no multihull is any cop uphill.

 

[dancrane]

Absolutely no offence or scorn intended, Mr McDoon. I'm well aware that modern cats and tris are thoroughly capable; but I rather like the comfortable and accommodating older types which, whatever their virtues, really don't seem to have had windward ability amongst their design criteria.

Granted there won't be many cheap, elderly, comfortable sub-25ft shoal-draft monohulls either, which can crowd on sail and squirt upwind in a force 5 at sea; but if an old catamaran can't sail off a lee shore, she'll need to be able to power off and the right engine must be a basic consideration.

I wasn't joking earlier, about LPG. Can most outboards be converted to run on it? Honda generators and Range Rovers can...So I'm guessing the whole boat could run on Propane.

 

[Lakesailor]

Thinks for a minute...

...so...the unashamedly modest horse-power of the Seagull was put to its best use as a low-geared, slow-running big-prop turner...

Wouldn't trolling outboards - or other electric motors, with their high torque at low revs - replicate the barge-pusher principle quite well?

What you need for ultimate torque at low revs is a steam-engined outboard