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Old 05 September 2009, 11:47   #1
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What size reserve outboard?

Hi, what is the smallest reserve outboard (ie HP) that will get a 5m-5.5m rib out of trouble?
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Old 05 September 2009, 12:15   #2
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Auxiliaries

Quote:
Originally Posted by martin33100
what is the smallest reserve outboard (ie HP) that will get a 5m-5.5m rib out of trouble?
I suppose it rather depends on how much trouble you are in.

However I must admit I have bee thinking about auxiliaries especially after a number of very interesting recent threads, “2 engines or 1”, and Alystar’s “The day the engine stopped” for example.

• I would be very interested to know
• What hp people have?
• What prop size and pitch?
• How they are set up?
• Who test theirs out and in what conditions?
• and how they got on?

I have a Yam 2stroke 6hp which just squeezes onto the transom without interfering with the main Opti.

A few weeks back I tested it in fairly sheltered waters about ½ ml offshore with about a 10kn breeze and a slight chop of less than a 0.5m. I strapped the aux into ahead and in general I was able to steer using the main engine leg surprisingly well. The best I was able to get out of her was 5kn which didn’t seem that bad however even in the slight chop the pitching was enough to cause the prop to get close enough to the surface to start aireating. This would cause her to drop of to say about 3.5kn before picking up again.

The next day we came across the same bay and round a headland we found ourselves pushing a 20kn breeze and a very short chop of about 1m. I didn’t try the aux as we had been out snorkelling for a couple of hours and we all wanted to get beck ashore. However I am pretty sure we would have made dismal if any progress and how we would have been able to steer I am not sure. I think the bow would have been knocked off and with little headway steering with the Opti’s leg would have been ineffectual.

I admit that I really must make the time to test this out in more demanding conditions and should have done so when I was out a few weeks back.

We currently cruise where the Pyrenees reach the Med the weather can be lovely but often very very localised. Finding a 20kn + breeze when you come round a headland is quite normal and from time to time I’ve been out and run into a fair bit more. Out of season I can have the whole place to myself seeing at best a distant trawler all day. So if I get things wrong and there is no easterly in the wind it is next stop Algeria or Libya but if I am lucky perhaps the Balearics.

I suspect my 6hp Yam the way it is set up is not up to the job but what do I do? Anything any bigger will take up too much room on the transom and interfere with the Opti. My understanding of the Yam 6 is that it is essentially the same as the 8 but just down tuned. So by going up I probably won’t gain much if anything and anyway you can’t get these 2 strokes new anymore. The 4 stroke yam is too wide to fit.

I think getting the prop lower would help and I could do this by cutting out the transom but I must admit I don’t fancy that as it may weaken the transom in general. I could be just inviting a whole load of problems. Also lowering the aux may put it in danger of swamping

An outboard bracket might be the way to go so I could get the aux lower in the water but I doubt if I could get an of the shelf one that would do the job.

I was also thinking about a different prop but am not sure which to go for.

Then of course I could go for replacing the opti with twins but I am not in the mood for that as I might just as well start from scratch with a new boat. To be honest I would feel more comfortable with twins but on a 6m? I would be better of going for a 7m + but that isn’t going to happen right now.

So what do others do or am I just asking too much from what is just a small auxiliary?

Your ideas please.

Jon
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Old 05 September 2009, 12:56   #3
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I believe the very unofficial rule of thumb is 1HP per M, plus 1HP

ie for a 5M boat it will be 6HP.

Nasher
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Old 05 September 2009, 13:05   #4
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I have a 3.3hp Mariner on my 5m Tornado

It just fits on the transom next to the 60hp and pushes it along
quite nicely. Ive not measured the speed but it took me back
into Christchurch Harbour against the current without to much
of struggle one one occasion.

Cheers

Paul
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Old 06 September 2009, 15:03   #5
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Engine size

The 6hp yamaha 2 stroke and 8hp 2 stroke are the same size / weight just one has been tuned, so can increase the Hp of a 6hp, would recommend a long shaft for 'wing' engine as is generally on the transom where there is more height.
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Old 06 September 2009, 15:45   #6
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Your thread is very interesting because after many years of thinking about a an Aux, I finally bought a Yamaha 2S Malta (3.5hp I think) from a mate but while it fits on the back of my Tornado 5m with a 60 Merc haven't actually tested it on the water yet.

Hopefully in the next couple of weeks I should get the chance to take it out.

How old is your Tornado?

Cheers
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Old 07 September 2009, 04:33   #7
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I had a wee 2Hp on mine last year. As has been said above fine for a slow chug back in naff all weather, but only if I sat on the toob at the strernto keep the prop in the water! I have since tracked down the 4hp "twin" longhsaft version - which should hopefully solve the "prop in the water" problem and being a 2 cyl version of the 2Hp, it is physically no wider so fits between the main lump & the frame. Pity they didn't do a triple cyl 6Hp! As the boat is in bits at the moment I can't test it to comment on the "real world" difference, but will try it as soon as I get back out (hopefully soon - watch out for a Humber refurb thread!)
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Old 07 September 2009, 08:25   #8
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I've got a 15hp 2-stroke mariner on my Ribtec 585 and that pushes it along at about 9 knots top speed. By contrast we used a 3.5 once to move a 6.5 Tohatsu RIB and that did the job quite well.
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Old 13 February 2010, 03:20   #9
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High Thrust or Saildrive an option?

Interesting thread as I just acquired a 5.4 Searider with a 20 year old Suzuki DT 115 strapped to the back. Though this engine seems to have an excellent reputation I want to be ready if this proves unreliable and was thinking about a long shaft 4 to 6 HP High Thrust or Saildrive engine. Any comments from those in the know?
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Old 13 February 2010, 03:34   #10
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Quote:
Originally Posted by Swordfish View Post
Interesting thread as I just acquired a 5.4 Searider with a 20 year old Suzuki DT 115 strapped to the back. Though this engine seems to have an excellent reputation I want to be ready if this proves unreliable and was thinking about a long shaft 4 to 6 HP High Thrust or Saildrive engine. Any comments from those in the know?
The ebay one?
You'll be lucky if you get anything bigger than 2hp on there without an aux bracket-which will stick out quite a long way astern. All I can get on my transom alongside the Yam and with an A-frame is a DT2.2. Even the old 4hp Evinrude twin or a Seagull (both very narrow) won't fit.
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