Whats the minimum aux engine I could use?.

[Jenko]

Festive Greetings,

New boat due to be delivered next week...Can't wait.

I'm think of getting an aux engine as a backup. What is the least hp I could get away with that would be of any use.

Boat is 6M long and 2.5m wide........

Cheers.

Paul.


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[BarryH]

Depends dunit. Where you gonna use it. On non tidal rivers you could get away with a tiny one, but that ain't gonna be any good if your going to try and push the boat up through the Run into Christchurch with the tide going out.
Whats the boat weigh. is it a displacement or a planing hull.

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[Dave_Knowles]

If you are using the boat in the Solent you will probably need 10 to 15hp. I have asked the same question becuase I have a 6hp which would only move my boat along against the tide at 1.5 knts which is not enough if you are trying to get home. If there had been any wind I would probably been going backwards. I would also say join Sea Start if you are in the Hamble area so if you are in real trouble you can always call them out and they will get you home.

The formula for working out the maximum speed for a displacement hull is:

the square root of the hulls waterline length in feet X 1.34

This gives you a rough guide to the maximum speed you can obtain trough the water. Something to do with physics I uderstand - or don't in my case.

It is worth remembering that the weight of a 9.9 and 15hp are normally the same so if you can afford it go for a 15hp.

I am sure that those with far more knowledge than me will explain it to you in further postings.

<hr width=100% size=1>Take care.

Dave

Dave Knowles
Southampton - UK

http://www.MyCleopatra.co.uk

 

[duncan]

5 hp

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[Jenko]

Thanks for the replies...

The boat is a planning hull fited with a 75hp 4stroke. All up it weighs around 1100kg.

I will be using it mostly around the solent, with the occasional poole / Chichester trip.

Being a sailor, I get a little paranoid having to rely too much on mechanics. Although the engine and boat are new.



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[BarryH]

I'd go for a 4 stroke of the same brand as the main engine. The the tank for the little engine can be used as a reserve ans if big engine breaksdown you can still use main tank for little'un. Id look for 5/6 hp. Won't be fast but should be able to get you home/keep you out of trouble

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[Dave_Snelson]

I agree with Dave Knowles. Remember that Sod's law dictates that if you are to suffer main engine failure, then it will happen on an outgoing spring tide. So... 15HP if you can afford it and 10HP should be your minimum.

Alternatively bolt a mast to it!

<hr width=100% size=1>Madoc Yacht Club
<A target="_blank" HREF=http://www.madocyachtclub.co.uk>http://www.madocyachtclub.co.uk</A>

 

[gimmesunshine]

Hi
I've got a 1400kg sealine 19 weekender and carry a 3.3 mariner for use on tender and possibly as reserve. I've used it in the shallows to get me out many times and it works well, can get 2.8 knots which is useful. However if I was in real trouble, ie wind and tide and bit of swell it would be useless. It would easily be swamped by any waves coming astern. I did have 4hp but was 10kg heavier and a real bind to haul in and out so It didnt get used. Might be best to get a 6 hp long shaft on a retractable transom type bracket and a decent lock.

<hr width=100% size=1>sunshine on a rainy day...

 

[truebrit]

My Old Bayliner 1952 is same size as your boat and about 1.2 tonnes displacement,and my ancient 5hp suzuki has rescued me against a 4 kt tide .

<hr width=100% size=1>Mike....... V8s are sweet music

 

[whisper]

I'd go for a 6-8hp 4 stroke, long shaft. Should get 5knts with the latter. Anything bigger will give you more power in reserve but will be too heavy to hump on and off the boat regularly.

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by whisper on 10/12/2003 23:52 (server time).</FONT></P>

 

[Dave_Knowles]

Going back to my experience a few weeks back the day was calm and we decided to go out fishing in the Solent. At about three o'clock the main engine died and I did everything I could to get it going. The tide had turned and was drifting us down towards Lymington and there was noone around so we put the 6hp Seagull on the backand started it. Our progress was maximum 1.5 knts against the tide and it was starting to get dark. This was a very scarry time. Fortunately as I saiid there was no wind for we would have been going backwards. I felt there was nothing else for it than to call Sea Start who cam out and towed us home. Don't go for an engine too small especially in the Solent where the tides can be pretty strong. If you need that engine it is sure to be at the worst time and you will be pleased to see 4 or 5 knts in a forward direction. It is easy to say a 5 or 6hp will do but I now have the tee shirt and my day ended fine but it was no thanks to the auxilary I though and had been advised would save the day.


<hr width=100% size=1>Take care.

Dave

Dave Knowles
Southampton - UK

http://www.MyCleopatra.co.uk

 

[duncan]

apples and pears

I stand by my earlier recomendation, although I agree with the sentiment behind Barry's comments.
Generally the weight, size and cost differentials between a 5 hp 2 stroke and a 5/6 hp four stroke will be substantial. If your current rig includes at least one 5 gall non fitted tank then I would carry oil and a fitting to enable the linking of it to the auxillary rather than have all the above factors against me. In practice you will not be using this to return home, only to a safe haven so having the capability to run for 10 hours isn't a major issue.
Comparing your craft with a Cleopatra is like comparing apples and pears - just doesn't hold.
My previous boat was just a touch larger than yours - 6m60 / 1400kg with a 175 OB and I had a 4hp /4stroke on the transom as well. It was adequate to get me home / out of trouble giving me 4.5knots through the water. With the benefit of this experience I would get a 5hp 2 stroke if I was repeating the exercise.
Barry's boat is also a good match for yours (again slightly bigger heavier) and he has used his 4hp/4stroke in a similar way.
They will also make an excellent tender OB being nlight and easy to handle and stow - and you should aim to get more use out of it in this capacity over the years than as a get you home!
Finally a new, modern, OB of your size really shouldn't fail - and you can even start a 75 by hand if you suffer battery failure.

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[Dave_Knowles]

Re: apples and pears

Duncan,

The law of physics come into play with the speed of a vessel through the water and my boat is a semi displacement hull and therefore will travel at about the same speed as any oither semi displacement hul of the same water length.

As for the 4.5 knts how were you measuring your speed and what was the weather like? Was the wind with you or against you? If I had been going with the tide I too would have been doing 4.5 to 5 knts, but I wasn't. If I had been at the mouth of the river it would have been ok, but I wasn't. If it had been the middle of the morning I would have probably gone on without calling for help, but it wasn't.

My feeling is that the sea is a very unpredictable thing and therefore I would prefer to have some power in hand especially as I often have other peoples lives in my hands as well as my own.

You have your views and I have mine.

<hr width=100% size=1>Take care.

Dave

Dave Knowles
Southampton - UK

http://www.MyCleopatra.co.uk

 

[duncan]

Re: apples and pears

firstly we are talking about displacement mode travel only here , and not even approaching the limits of that so lets leave all that out of it please. However your boat will not travel as fast (through the water) with (say) a 3 hp as Jenko's because it is bigger and heavier. You would probably both travel at pretty much the same speed with a 15hp in calm conditions as discussed in detail in repsonse to your own post a month or so ago.
Secondly I clearly stated 'through the water'. In general windage is a function of weight and length for mobos and, whilst a factor, is consistent in the overall equation. Conditions such as waves will have a variable effect but, as long as drive itself remains (prop in the water!), they will average out. Certainly in any seaway a larger auxillary will deliver more thrust and therefore be more capable of keeping a craft going into a head sea and or wind but you can have the same issue with your main engine at times and changing course is often teh solution! Finally I agree fully with 'your feelings' and we spent a lot of time discussing the issues and factors for you and your boat - which all seem to have been born out in practice. Jenko does not however have a Cleopatra 700 and, for all the reasons gone into in the responses to your post, would be better off with a smaller lighter engine than you require to acheive the same ends.

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[Dave_Knowles]

Re: apples and pears

Duncan,

I am sure you uderstand physics better than I but all I can say in my defence is this is what I have been told. The other thing I would point out is when i asked the same question about the size of an auxilary out board for my boat and many people came back and said that I would only need 4 or 5 hp and now I find having spent out over £300 on a 6hp engine it is too small so I am just trying the help others avoid the same thing happening to them. I know you suggested a 9.8 Tohatsu before you come back at me but you also said:

"Better to use the anchor when appropriate - ie. drift out of a hazard or into shallow(er) (7-10m is good). You can then decide what course of action to follow without time pressures. This is also of course where radio comes in very handy !
If you are out in open water you will also be surprised how quickly you cover ground with wind and tide - anchor when they are against the direction you wish to travel and take the free ride when in favour. It wouldn't be unrealistic to get from say Old Harry back to the Needles on one tide, then cadge a tow back into the Solent.
(1) quickly anchor when safe to do so
(2) assess all the factors (including crew!) try to repair
(3) call coastguard and discuss"

But if I had sat it out until the tide changed it would have been about 9 o'clock at night but we would have then managed to get our magic 6 knts out of the outboard.

Maybe the best way to answer Jenko's question is for him to try out a small outboard and find out if it is ok. Maybe it will be.

<hr width=100% size=1>Take care.

Dave

Dave Knowles
Southampton - UK

http://www.MyCleopatra.co.uk

 

[extravert]

A similar size rag boat which uses an outboard as its only engine would have 6 to 10hp, and would typically get about 5 knots. I know they probably have less windage, but they have bigger displacement. Maybe that's a good guide.

<hr width=100% size=1>One day, I hope to own a real boat.