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

[dancrane]

This is a very idle question. I don't need to know, I'm just dreaming about bigger boats because I'm not free to work on the dinghy.

I know several manufacturers make very-long-shaft outboards, and some offer lower gearing and bigger props to suit the weight and sloth of ballasted hulls.

I seem to recall some manufacturers giving such engines a particular name, to differentiate from their usual market & range. Anybody remember the name or type?

Are certain brands credited with really having worked out the appropriate gearing? Most websites seem fairly vague, leaving prop preference to buyers.

The protected security of inboard diesels chugging away in small yachts is appealing, but there seem to be so many associated problems, so often, plus the considerable weight, space, propellor drag and cost that diesels represent...I begin to like the idea of an auxiliary that could run on the same LPG as the stove & heater.

Most yachtsmen with outboard auxiliaries seem not to have worried for long about whether the engine's gearing is really suitable for its purpose...

...which must encourage loyal fans of those hefty, intractable old inboards which would cost more to replace than the vessel is worth.

 

[Davy_S]

Seagull

 

[dancrane]

No!

Let me close the door right away, on all attempts to promote any foul, old, oily ear-shatterers. Or fowl old smelly 5hite-spatterers. Seagulls, British or otherwise.

 

[Davy_S]

I suppose it will have to be an Ocean 4 or Ocean 8 then.

 

[TQA]

Tohatsu do a 6hp extra long shaft, 25 inch, with a larger dia low pitch prop. Sometimes called the Sail Pro. See http://www.onlineoutboards.com/Tohatsu-6-hp-MFS6CSPROUL.html


However on a head to head tug of war with a Seagull Barge Pusher my money would be on the Seagull.

 

[Tranona]

No!

Let me close the door right away, on all attempts to promote any foul, old, oily ear-shatterers. Or fowl old smelly 5hite-spatterers. Seagulls, British or otherwise.

Despite that it is still the most effective outboard for the job at low (sub 5 knots) speeds in terms of converting power to forward motion. That is because it starts with a large diameter fine pitch prop turning at very low speed. "Modern" outboards are simply unable to do this as their basic architecture prevents them swinging a large prop. The output shaft speed is too high so you end up with the engine having to produce a lot of horsepower to drive a small prop.

Most of the main brands have at some time or other produced compromise engines with either bigger props or bigger reduction ratios (or both). They usually put "Sail" something in the model name.

 

[dancrane]

Thanks Mr T; that's certainly clearer. But I wonder why the product has largely disappeared, when the need for it still exists?

Plenty of yachts under 25ft use outboards, but few of these motors can have been designed particularly with high thrust and low maximum speed in mind.

Were the "barge pusher" type of engines embarrassingly thirsty? They must rev pretty high despite the boats they drive necessarily going slowly.

 

[Seajet]

Dan,

if one really must the preferred longshaft 4 stroke engine for Anderson 22's is the Tohatsu Saildrive 6hp; along with bigger prop's these come with an uprated charging coil, 6 instead of the usual 3 amp, and of course external fuel tank.

I bought my 2-stroke Mariner 5 at Southampton boat show, as my A22 chum & neighbour was buying the same we got a deal.

We have both removed the internal fuel tanks to reduce weight a fraction ( surprisingly when I lifted an identical engine with empty internal tank I immediately felt the difference ) and as we maintain our engines scrupuously we wouldn't dream of the weight of a 4 stroke, let alone the stowage / hydraulic locking issues.

As for fuel consumption, I have happily motored across the Channel - 80 NM - with fuel to spare, using 1 gallon tanks and a splash proof funnel to top up en route; I get 2.5 hours per gallon.

 

[fergie_mac66]

extension kits

Thanks Mr T; that's certainly clearer. But I wonder why the product has largely disappeared, when the need for it still exists?

Plenty of yachts under 25ft use outboards, but few of these motors can have been designed particularly with high thrust and low maximum speed in mind.

Were the "barge pusher" type of engines embarrassingly thirsty? They must rev pretty high despite the boats they drive necessarily going slowly.

you can buy extension kits for most outboards I have done 2 converting a long shaft to an exlong shaft. It takes a couple of hours to do and with the addition of a hi-thrust prop makes a big difference. If you want exlong you have to start with a long shaft outboard. Edit but then you need a kit with a shaft extension not a one piece shaft

http://www.baymfg.com/kits/mercury/

 

[fergie_mac66]

Thanks Mr T; that's certainly clearer. But I wonder why the product has largely disappeared, when the need for it still exists?

Plenty of yachts under 25ft use outboards, but few of these motors can have been designed particularly with high thrust and low maximum speed in mind.

Were the "barge pusher" type of engines embarrassingly thirsty? They must rev pretty high despite the boats they drive necessarily going slowly.

Some of the manufacturers make them as kits supplied to order from new but a lot are not available in uk and you have to import them with HMRC sticking an import tax on.
5 or 6 inch kit consists of few parts and can be done in the same time as changing a water pump tho you have to be carful as they are fiddly


There are a lot of kits available on ebay
typical example

http://www.ebay.co.uk/itm/JOHNSON-SUZUKI-4-5-6HP-FS-LONG-SHAFT-EXTENSION-KIT-LEG-/280281447457

 

[fergie_mac66]

we got our last kit from these they were slow to supply but the kit was good

http://www.marineparts.com/partspages/accessories/acc8.htm

 

[Giblets]

Another vote for the Tohatsu 6HP saildrive outboard.

As it happens I do know of one for sale if anyone is interested!

 

[stephen_h]

Yamaha make a 9.9 with high thrust and extra long shaft. Used a lot on catamarans (as we do!)

 

[Niander]

I have a seagull bargepusher they have a 13" prop!
wonderful if you can find one they are quite rare
sometimes pop up on fleebay

 

[propnut]

I agree that Seagulls are good basic engineering,what nobody has commented on there ability to stop a heavy boat moving in a forward direction.In my opionion the old Chrysler saildrive was a great bit of kit.They used a 45hp gearbox coupled to a 9.9 hp motor..
Mariner are the only ob company to anywhere near with thier bigfoot range

 

[dancrane]

I wonder if there's a practical way to calculate the amount of thrust produced by an engine like the Seagull BP?

I can't pretend I've ever understood the difference between torque and power (if anyone feels like explaining, best to keep it brief!)...

...but I'm guessing that a little prop turning at high revs, produces a narrow jet that's ideal for powering lightweight craft at speed; whereas a big slow-turner shifts just as much water, but in a broader, slower current, hence it's not really trying to accelerate the vessel, just to make sustained thrust?

If really big slow props are better for displacement hulls, why do most sailing yachts have such little ones?

 

[ffiill]

Seagull

Second that-I recently picked a century plus 6 bladed for £60 as an emergency aux.for a 28 footer with a suspect engine.

 

[AngusMcDoon]

Yamaha make a 9.9 with high thrust and extra long shaft. Used a lot on catamarans (as we do!)

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

 

[CAPTAIN FANTASTIC]

I use a Tohatsu 6hp four stroke long shaft as a back up for my heavy Macwester Wight and also used on my inflatable; had it for over 8 years; powerful, reliable and economical.

 

[Tranona]

I wonder if there's a practical way to calculate the amount of thrust produced by an engine like the Seagull BP?

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 motors to demonstrate the "pulling power" (no, not that sort) of 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.

The main reasons why Seagull eventually disappeared were environmental and high cost. The sailboat and small workboat market is a tiny proportion of the overall outboard market, so not worth a dedicated engine. Modern engines do quite a reasonable job - and are quiet, smooth, clean - and have reverse gears which few Seagulls had.

Progress - of sorts.