Tender outboard - external fuel tank?

[neil1967]

I will shortly be buying a 6HP 4 stroke outboard for my 2.75m inflatable keel dinghy, to be used as a yacht tender, hopefully for a liveaboard somewhere warm. I'm inclined towards a Suzuki DF6A, which seems to be the lightest (and I'd value any opinions for/against); however, what I'm interested to know is whether it is worth having an external petrol tank? The internal tank is 1 litre - how long might I expect that to last in ordinary use as a tender - I know it's a bit of a difficult question, but I have no idea whether it will gulp petrol and perhaps last 30 mins or sip it and last 2 hours? I know I can always add a tank later, but for various reasons it would be more convenient to buy it as a job lot if I need one.

 

[Binman]

Hi, you should be able to find out about fuel consumption on line, Depending how far you intend to travel in it I would just keep the small tank for ship to shore.It seems a large engine at 6hp for a inflatable difficult to lift of and on?

 

[duncan99210]

I agree that 6hp is perhaps a little large for an inflatable. More normal to see something between 2.5 and 4 hp on a 2.75 dinghy.
As for fuel useage, when we had a 2.5 four stroke using it every day several times a day for ship to shore the tank would last about a week: not too different with our current 2 stroke engine, but that is a little thirstier . If we were using it for a long trip, simply take the spare fuel can with you and refuel as required.


L

 

[TQA]

Be aware if thinking about the Carib that Suzuki spares are not as easy to come by as Tohatsu/Nissan or Yamaha.

Go for the remote tank if you can.

 

[yotter]

I have a 6HP Mariner (2014) on a Zodiac 285 (9 feet in old money), I normally use an external tank around 20 litres. This year I seem to have been using the internal tank a bit more, mainly due to concerns about dirt in fuel (about 1 litre?), and have run out of fuel a few times. Fortunately I have always had a spare 5 litre can with me. These 4 strokes can be very economical, but I think my running out of fuel has been due to underestimating fuel consumption which is a function of speed! So, my fault. My advise would be either get an external tank, or carry a spare 5 litres in a can.
Angus

 

[jac]

Interesting size OB. It will get your dink onto the plane with 1 on board but may not with 2. ( our 5hp 2t gets our 3.1 airdeck on the plane with just me on board - nearly 15 stone)

It might be worth reviewing that. Many airdeck owners go for 9hp+ as that will get the tender on the plane even with 2 and some luggage.
if planing is not relevant to you and you will be 1 or 2 up then maybe a 4hp

If you want something that will enable a quick blast then go for the 6. As for how long it will run on 1 litre, i expect not long. we had a 2.5hp 2t that burnt 1.4lph at full chat. our 5hp 2t is about 2lph. I know that typically a 4t SHOULD be more efficient but at full chat i wouldn't expect 1 litre to last more than 30-40 minutes. Fine if you're 5 minutes from the quay and just going back and forwards once or twice a day but if you're doing more, then go for the external.

 

[Ademist]

If “somewhere warm” is the Caribbean, then I would definitely go with an external tank. A 10 L tank lasts us up to four weeks with our Yamaha 6hp, and means we are not worried about refuelling, which isn’t available everywhere.

We took across the 6hp outboard with a flat bottomed inflatable, but after a season bought an aluminium rib (as do a lot of people). We wished we’d bought a 9 or more hp outboard, as we frequently travel much longer distances than we did in Europe and with more people on board. The 6hp outboard works, but bigger would be quicker and more comfortable.

 

[James_Calvert]

We've got a 4hp 2 stroke which has the facility for a remote tank. For longer expeditions it was well worthwhile.

However the tank was a pain to store and was more likely to leak than a simple can so we don't use it that way any longer.

 

[billcole]

If you don't go for the external tank then I've found it useful to have a smaller than 5 litre spare can.
Aluminium fuel bottles sold to carry camping stove fuel in come in 0.5-1 litre sizes, smaller to stow in the dinghy, easier to hold over the stern to refill the outboard, and if there's less capacity in your bottle than there is space in your outboard tank you can just tip it all in without keeping looking to see if it's about to overflow.

 

[dom]

I use an 8hp Yam 2t (c.27kg) on a Zodiac 360 which easily planes three-up (60kg av wgt) and the big tubes make it feel safe in a chop.

This only has an external tank, enabling one to safely store a dry-engine in a stern locker and the petrol in either the vented gas, or windlass locker. Clean, safe and easy.

 

[No Regrets]

I use a 1 litre aluminium bottle as emergency rations on the basis it suffices and takes up no real space! (Mercury 3.5hp)

 

[neil1967]

Thanks for all the input - useful. 6HP is the most powerful single cylinder 4 stroke outboard. All the 4,5 & 6 HP engines from each manufacturer are essentially the same weight (in the case of the Suzuki, 23Kg), so there is no weight penalty for increased power. Going any larger (typically 8-9HP) involves moving to a twin cylinder, with weights typically starting at around 40Kg - quite an increase for hauling on and off the yacht. I reckon a 6HP on my 2.75 dinghy will definitely get us on the plane with one on board, and possibly two-up. Thanks again.

 

[James_Calvert]

Have you thought about a 2 stroke? There's a similar weight step between 1 cylinder and 2 cylinder versions, but the Tohatsu is only 27kg, all the way up to 9.8hp.

Of course it would be screaming away at over 5000rpm delivering that power which might be another consideration!

 

[geem]

Have you thought about a 2 stroke? There's a similar weight step between 1 cylinder and 2 cylinder versions, but the Tohatsu is only 27kg, all the way up to 9.8hp.

Of course it would be screaming away at over 5000rpm delivering that power which might be another consideration!

The Tohatsu 9.8hp two stroke is a fantastic engine. Fuel efficient and quite. We moved up to a 15hp Yam. Heavy on fuel and very noisy compared to the Tohatsu. Having owned a Mercury 6hp four stroke, the Tohatsu 9.8 two stroke is in a different league

 

[GrahamM376]

Have you thought about a 2 stroke? There's a similar weight step between 1 cylinder and 2 cylinder versions, but the Tohatsu is only 27kg, all the way up to 9.8hp.

Of course it would be screaming away at over 5000rpm delivering that power which might be another consideration!

We can plane at 17 kts with our Tohatsu 9.8 2 stroke, which replaced a Suzuki DF6 which was nothing but trouble. That had 2 replacement props after the bushes failed (no I hadn't grounded the props) 2 x filler caps after the internals rusted away and the engine paint fell off a couple of months after warranty ran out. Wouldn't consider another, whatever the price. Much prefer lighter second hand 2 strokes than heavy equivalent power 4 strokes.

edit - forgot to mention Suzuki was a bad starter, particularly when warm.

 

[jac]

We can plane at 17 kts with our Tohatsu 9.8 2 stroke, which replaced a Suzuki DF6 which was nothing but trouble. That had 2 replacement props after the bushes failed (no I hadn't grounded the props) 2 x filler caps after the internals rusted away and the engine paint fell off a couple of months after warranty ran out. Wouldn't consider another, whatever the price. Much prefer lighter second hand 2 strokes than heavy equivalent power 4 strokes.

edit - forgot to mention Suzuki was a bad starter, particularly when warm.

The Tohatsu 9.8 2t is the OB of choice for Sibbers and so does command a premium.

 

[CliveF]

Mine was put on the back of an old 15' heavy fibreglass open boat. I tried it on the internal tank first. I was at about 1/2 throttle to achieve hull speed and the tank lasted about 20 minutes. Thankfully I had spare juice with me as i was expecting much longer and had not realised just how small the internal tank was.

An inflatable tender should skim over the surface , even so i would not expect more than 30 min max.

With an external tank it runs for ever. It is a good engine and I am pleased with mine.

Regards Clive

 

[Quandary]

We can plane at 17 kts with our Tohatsu 9.8 2 stroke, which replaced a Suzuki DF6 which was nothing but trouble. That had 2 replacement props after the bushes failed (no I hadn't grounded the props) 2 x filler caps after the internals rusted away and the engine paint fell off a couple of months after warranty ran out. Wouldn't consider another, whatever the price. Much prefer lighter second hand 2 strokes than heavy equivalent power 4 strokes.

edit - forgot to mention Suzuki was a bad starter, particularly when warm.

I had one of those as back up on a motor cruiser, lighter than a 6hp four stroke and lots of torque with the right prop fitted, they are like hens teeth in the Uk because of the fuel regs.

 

[Graham376]

Cancelled, duplicated post

 

[QBhoy]

Try and find a good Yamaha 8hp 2 stroke and be done with it. Same weight as the gutless 6hp 4 stroke you have in mind and will plane with 2 up. The 6hp you are considering likely won’t.
Not easy or cheap for a Yamaha 8 thoogg. For this very sought after reason. All the best.