Auxiliary long or short shaft?

Rich L · 27 May 2004, 09:19

Presumably if I'm thinking of buying a small auxiliary engine for my boat it will need to be long shaft right?

Thanks

Rupert Bear · 27 May 2004, 10:35

Not necessarily, mine is short shaft cos when I originally bought a long shaft it was too long and trailed in the water. The Vee of the hull is shallower at the side so the short shaft was long enough.
Only way to tell is to measure the angle the engine will hang at and the length and see where it will come down to.

Headhunter · 27 May 2004, 10:37

Rich

I have a Yamaha 4hp 2 stroke short shaft auxillary fitted on to an adjustable mounting bracket, which works fine.

As it is only a get me home back-up I am not too worried that the shaft is a little short.

As long as there is decent drive and the cooling intake is adequately covered a short shaft will suffice.

Take care chosing and siting the bracket.
Make sure the vertical movement is enough to raise and lower the distance required.
Don't forget to ensure turning clearance for your main engine when the auxillary is in both up and down position.

I have a fuel filter for my main engine with an additional fuel line with priming bulb for the auxillary as my main engine fuel fitting is a fixed fitting.

Although my Yamaha 130 is autolube we also premix 100:1 (as advised by my Yamaha service provider) to give extra protection so this fuel is also OK for the auxillary.

I hope this is of some help.

I suspect I am a few weeks ahead of you in fitting out, for you appear to be encountering the same questions I have recently dealt with.

John

Pete7 · 27 May 2004, 10:54

Quote:

Originally Posted by Headhunter

Although my Yamaha 130 is autolube we also premix 100:1 (as advised by my Yamaha service provider) to give extra protection so this fuel is also OK for the auxillary.

John,

over oiling a 2 stroke can be as bad as not enough. What happens is the extra oil burns creating extra ash/soot which builds up under the piston rings forcing them out creating hot spots on the bores.

Those v4 Yamahas as superb engines and mine ran for 14 years without problems.

Pete

Rupert Bear · 27 May 2004, 11:59

I would be more worried running the aux on 100/1, are they not usually 50/1? Mine certainly is.
You also have to be careful with aux brackets, they are not meant for RIBs that bounce all over the place at high speed. I would recommend some sort of ratchet strap holding it down rigidly and not rely on the locking pin or even the pivot holding the engine to the bracket.
I didn't buy one of the moveable brackets but a fixed one rated for a much larger outboard then cut it down smaller and use a strap round the main part of the outboard to hold it down rigid.
I did have a lighter duty version but things started to bend and break within a few weeks of first using the boat.

Nick Hearne · 27 May 2004, 12:33

Quote:

Originally Posted by Rupert Bear

I would be more worried running the aux on 100/1, are they not usually 50/1? Mine certainly is.

Hi I have a Yamaha Malta 2 stroke that runs on 100/1.
I also have a Johnson V4 which I have been told is the same engine as the Yamaha, it is 12 years old & touch wood the autolube has not given me a hitch!
Nick

Richard B · 27 May 2004, 13:09

Our auxiliary is a long shaft... it just depends on the configuration of your boat and position of the mounting bracket. Time to get the tape measure out, Rich!

Headhunter · 27 May 2004, 13:52

I would be more worried running the aux on 100/1, are they not usually 50/1?

Rupert

Yamaha handbook for 2B, 3A(MALTA),4AC, 4BC, 5C are all 100:1 mix ratio.

Pete

The advice to premix the autolube comes from a service engineer who supplies many of the North Sea Oil industry safety boats only with Yamaha.
They all adopt this premix routine and there has not been a single warranty claim in at least 15 years on the Yamaha's supplied with many doing at least 4000+ hours of service before replacement.

I will ask my service guy about your hot spot concerns and report back.

John

John

Matt · 27 May 2004, 14:21

I agree with premixing at 100:1 on an oil injected engine. Oil injection, at least on the older mercs, was notoriously unreliable due to the plastic gear on the crankshaft. At least with 100:1, you can suffer an oil injection failure and the engine won't get trashed instantly. IMHO relying on oil injection on any high hours engine is a lottery, and splashing some oil in the fuel is cheap insurance.

I disagree with running an aux engine on 100:1. That's so little oil you get sod all corrosion protection, and for an engine that's going to spend most of it's life sitting around getting damp, the more oil the better IMHO. Plus the one time you really really need it, it probably won't have run for months and the bearings & bores will be dry. But since you're probably in deep shit already by losing the main engine with the QM2 bearing down on you, you rather want to be able to start the little begger and give it some ASAP. I know they CAN run on 100:1, and quite happily, but in the same way the main engine doesn't NEED an extra bit of premix, it's good insurance.

I also disagree with the aux fuel source being from the main tank. If you take a wave on board, or fill up from the cowes barge after a storm, it's quite likely that the main engine failure is from water in the fuel. If you're going to design a system with redundancy, the fuel systems must be completely isolated too.

That's not to say however that the aux cannot be switched to also run from the main tank, or vice versa (main engine from aux supply) but just that the primary supplies for each engine should be wholly independant.

Matt · 28 May 2004, 21:17

Well I killed that one good and proper didn't I.

nick wood · 28 May 2004, 21:59

Read June's issue of Motor Boat Monthly, right up on What Auxiliarys to have. hope it is some help.

Rich L · 29 May 2004, 22:52

Thanks everyone for the good advice.

Rich L

Rupert Bear · 30 May 2004, 23:43

Sorry missed the last few days as I was diving in the Summer Isles. My Tohatsu runs on 50-1 mix as per handbook. I agree with running it rich as well.

ribfreak · 01 June 2004, 12:23

I run my little Volvo 4hp also on 1:50 and would do so with any other aux as well- since an auxilary is a rather small engine compared to the boat size, it`s likely that it`s operated almost any time at full throttle to just give your RIB a minimum of speed and manouverability! Even all the variable-ratio selfmixing engines of today go down to that ratio when they have to run WOT, so the little aux will easily be capable of burning the oil, no probs at all! If you plan to use a slightly bigger motor also as a kicker for trolling at medium speeds we have another situation...
greetings,
Wolfie