Auxiliary engines

Pat Willan · 13 June 2001, 17:15

Being somewhat of a newcomer to ribs (don't know why I left it so long) I may be trying the patience of the more experienced on this subject.

I keep getting conflicting advice on whether to fit an auxiliary outboard or to spend my money on something else. For a 6.5m. rib (200HP. Optimax main engine) the extreme views range from "only a 15HP. unit will do" to "you are better off attaching chain to it and using it as an anchor"!

With coastal cruising around N. Wales and the occasional longer (70nm.) open sea leg in mind what is the considered view. Any help will be gratefully received.

I'm awaiting delivery of a Tornado in July - can't wait to get into the Menai Straits.

Pat.

Charles · 13 June 2001, 22:49

Basic rule of thumb : for every metre of boat you have, you should have the equivalent in HP.
That is 5mtre RIB = 5HP Aux. Give or take, also depends on your sea conditions, tidal flow etc.

Alan · 13 June 2001, 22:54

I'd agree with that as a rule of thumb although we only have a 5hp Aux on a 6.5m RIB. Top speed is about 4-4.5kts so going against the tide is probably not an option!

Pat Willan · 14 June 2001, 09:29

Thanks for the replies.

On a more fundamental level clearly you feel that auxiliaries are a good idea - I should have thought so as well, but both the boat builder and an RYA instructor said not to bother with one at all!

Pat.

tsunami · 14 June 2001, 16:28

Hi there,
In the past I built many ribs of various sizes and for various applications. Over all these boats it was probably about a 50/50 split as to having an auxillary or not!
I have a 7m rib with a 225hp outboard on the back and I decided not to bother with an auxillary, I did however fit a very good VHF, I also carry at all times a handheld VHF, a good selection of flares, a sea anchor and various other items of safety equipment.
The main reason for deciding against the auxillary engine was to do with an excercise I was invovled in along with the Coastguard which took place off the North Irish coast.
The excercise involved setting over twenty boats adrift at a known position and monitoring their positions over a 6 hour period! There were various boat types and sizes used for this excercise, mainly fishing boats, sailing boats and ribs between 5 & 8 metres.
After a short period of time it was obvious that the Ribs were moving a lot faster that the other boats involved. If I remember correctly they were covering over double the distance compared to some of the other boats in the test. This was due to the windage that they were catching and the shallow draft. Although there was quite a lot of wind on the day of the test it was still quite calm.
From this I decided that unless you could guarantee a speed of around 8 - 10 knots to beat both wind and tide then there was little point in having an auxillary. To have this sort of speed you would need quite a big engine which then leads to the problem of storing it and mounting it when needed as I don't agree with hanging big auxillaries of the back of Ribs as a permanent feature when you see the thrashing they take!
Personally I feel if somebody is concerned about a second engine they should fit twin engines from day one, as running on one will give you a reasonable turn of speed. If you don't go for twins then I feel that it would be more important to carry all the necessary safety equipment and be confident in the use of a VHF radio!

------------------
Joe

GED · 14 June 2001, 17:14

LIVING IN THE N.WALES AREA I ALSO THINK IT IS BEST TO HAVE A GOOD RADIO AND ANCHOR.HELP IS NOT FAR AWAY IN THIS AREA.I HAVE A 8 MT. IN CONWY.

Charles · 14 June 2001, 18:16

I could not agree more with Joe! Twin outboards on a RIB is probably the safest way to go to sea, and that goes for all vessels.

Pat Willan · 15 June 2001, 09:44

Just a word of thanks to all those that posted their views on this subject - I shall have to agonise for a couple of weeks, though the attraction of dispensing with an auxiliary (saving the weight and the money) is great. I intend to have on board a VHF, flares, chain and substantial anchor, etc. in any case.

Perhaps I suffer from too vivid an imagination when it comes to disaster scenarios!

Pat.

[This message has been edited by Pat Willan (edited 15 June 2001).]

David Perry · 18 June 2001, 22:32

1.The RYA Instructor who gave such poor advice needs to have a serious rethink.

2. Not every one can afford a twin set, although nice to have, they add weight to the boat and a big hole in the balance.

3. An auxillary engine is desireable, I agree also with the advice given re HP per meter.
4. Don't try punching The Swellies with a 6.5 engine, it will not work, and you will be at The Ferodo Factory in no time at all! (Local speak for those who have no idea what I am on about)

5. The carrying of safety equipment should not even come in to the equation, it should be carried whether you have one, two or 6 engines.

6. The most important factor in all of this is training, local advice and advice from those who should know.

7. Enjoy Menai and keep the boat sponson side up!

Dave

Alan · 19 June 2001, 10:25

Its an interesting topic this and one I suspect that we all have fundamental views on we might not change!

My perspective is that even only being able to average 4-4.5kts is better than no aux. Many sailing craft make passages at that speed. Clearly one has to be aware of the tide and recognise the futility of trying to fight it, so there may be occasions where its essentially useless - although maintaining ones position whilst waiting for rescue surely has got to be a good idea, if you are in communication with the rescue authorities?
Preventing drift into an area of hazard - rocks, shipping lanes etc has also got to be worthwhile!

We have only used our aux in anger once - in the solent, approx 2 miles off Portsmouth harbour when the main engine expired terminally. Without the aux, although we were in no danger, we would have been forced to radio for help, which could have lead to the cost of a lifeboat launch etc. (Who would be better employed attending to reall distress.) That being said, it was a real struggle to get into Portsmouth harbour against the spring ebb!

The other factor might be age/condition of your main engine. Ours was a 87 model Johnson, which although regularly serviced, we were never as confident in as we are with our shiny new Merc Opti. (Hopefully not misplaced.) Of course IF I did all of my boating in more hazardous waters (such as the Channel Isles) and IF I could afford to buy, maintain and run twins then I probably would. Interesting thing with twins is just how big do you need each engine to be to maintain a planing cruise on one engine? I suspect on many boats this would be an issue.

Anyway, as I say I'm sure we all have strong views on this subject, these are just my 10c!

Cheers, Alan

Charles · 21 June 2001, 20:32

Interesting point ..... (.. thing with twins is just how big do you need each engine to be to maintain a planing cruise on one engine? I suspect on many boats this would be an issue.) My previous RIB, being the Hysucat 6.5 with twin Yam 4/stroke 50's, hopped onto the plain with one engine and managed 17knts comfortably! I suppose she was the exception more than the rule. It would indeed be a worthwhile exercise going to the manufactures and posing this exact question !? Any comments, Scorpion RIBS?