aux engine

zenair · 27 October 2016, 18:22

hi I am looking for some advice on what size of aux engine to fit and wether it needs to be long or short shaft. The boat is a 5.8mtr tornado with a 80hp Yamaha four stroke, any advice would be greatly appreciated.

beerbelly · 27 October 2016, 18:34

ideally you would want a 6hp long shaft I would have thought

A1an · 27 October 2016, 19:02

I used to have a 5.8m Northcraft and I used a 4hp Suzuki 4s as an aux. Tbh I never used it in rough waters but it pushed the boat along nicely.

On a separate note..... How does the Yam 80 push the Tornado along? Fuel consumption? Cruising speed?

zenair · 27 October 2016, 21:56

hi the yam and tornado for me are a perfect balance of power and economy it cruises at 23knots at 4700 revs and returns about 18 to 20 ltrs per hour depending on loading. I really enjoy the combination of both. Thanks for your advice on the aux engine. regards joe

Xk59D · 27 October 2016, 22:04

are you sure about those numbers?

that is a lot of revs for not a lot of speed with big fuel burn relative to the speed IMO, i wouldn't have thought an 80 (although borderline power i guess) on a 5.8 would have given those type of numbers.

my old 5.6 (avon) with a mariner 100 4 stroke was about 3800rpm at 23knots and it was probably about 16lph. very different boat granted but was a heavy bus due to the layout.

what revs are you getting full chat?

re the aux- 1hp per meter is the normal recommendation buddy. your bigger problem might be fitting one on though so take the boat somewhere to try diff sizes (clyde outboards has good range and you can drive boat right in there)

GuyC · 28 October 2016, 06:55

If you measure from the top of the transom or where you intend to put the outboard to the bottom of the transom, this will give you the shaft length.

With a deadrise hull, moving the outboard outboard will decrease the shaft length required.

As Xk59D says, the general rule of thumb is 1hp per metre.

I'm going through the same process and I'm bearing in mind that I'd like to use the same outboard for an inflatable tender so that may be worth considering.

Nice boat name.

jeffstevens763@g · 28 October 2016, 08:57

i had a 4hp suzuki on my 6m rib 5 knots tops good conditions just got it in on the transom, did have it on two transom brackets end on but found i could steer ok with the main engine as a rudder and leave it fixed,
it was short shaft because i used it on a tender but it was far enough up the deadrise to be in clear water.

zenair · 28 October 2016, 21:20

thanks to everyone that replied for the advice, very much appreciated.

breezeblock · 28 October 2016, 22:11

the other way of looking at it is any engine no matter how small it is going to be way better than paddling even my pissy little 2.3 Honda can go faster than 2 people giving it plenty with a paddle

Ron Noco · 29 October 2016, 21:53

Something to keep in mind, I didn't realise it myself up until I needed the aux engine , if you haven't allowed much distance between the engines you can only turn in one direction as the tiller arm gets in the way ....