What size reserve outboard?

martin33100 · 05 September 2009, 16:47

Hi, what is the smallest reserve outboard (ie HP) that will get a 5m-5.5m rib out of trouble?

Jon.esp · 05 September 2009, 17:15

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

Nasher · 05 September 2009, 17:56

I believe the very unofficial rule of thumb is 1HP per M, plus 1HP

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

Nasher

TUFTY · 05 September 2009, 18:05

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

badbaws · 06 September 2009, 20:03

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.

davej · 06 September 2009, 20:45

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

9D280 · 07 September 2009, 09:33

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!)

Tim M · 07 September 2009, 13:25

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.

Swordfish · 13 February 2010, 08:20

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?

Nos4r2 · 13 February 2010, 08:34

Quote:

Originally Posted by Swordfish

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.

Swordfish · 13 February 2010, 09:41

The ebay one? Yes the e-bay 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

Thanks this is helpful. I have an old Seagull and was going to give it a try so I'll have a rethink. What do you suggest I look for? I have an aux bracket.

Knot Yet · 13 February 2010, 09:57

Biff was more than happy that our little 3.5 aux would get us out of trouble if needs be - we have a 5.4m Searider, he is currently fitting an aux bracket which required some clever work as there isn't really room to mount it next to the main outboard.

From our experience of the main engine failing the aux would have got us to a safe haven to moor and wait for help - so from our experience much recommended

spartacus · 13 February 2010, 10:08

I have a Tohatsu 3.5hp on the back of the Zodiac Pro 4.2m. It's mounted on a Plastimo stainless steel bracket. The bracket itself had to be altered slightly due to the angle of the stern to get it over the side. The nylon auxilliary transom plate then had to be removed and cut down to size so I can turn the main engine hard lock both ways. Rattles about when in the raised position so I attached a ratchet strap to tension it underway. In the down position I can fix it in a straight ahead position and steer with the main engine. Does the job, but again I really need to test it throroughly, so I know what to expect.

Was looking for a Yamaha 4hp (2-stroke), but this proved difficult to find in a reasonable condition. The Tohatsu 4hp 4-stroke is simply too wide. The 3.5hp Tohatsu is slim and lightweight, hence my decision.

Nos4r2 · 13 February 2010, 10:13

Quote:

Originally Posted by Swordfish

The ebay one? Yes the e-bay one.

Thanks this is helpful. I have an old Seagull and was going to give it a try so I'll have a rethink. What do you suggest I look for? I have an aux bracket.

Is the bracket already fitted? If so, I'd be looking at a 3.5 to 4hp 2 stroke. much more weight offcentre and behind the main engine will be noticeable.

Is your DT115 premix or autolube? If it's premix, get an aux that runs on the same premix as the main engine. There's various easy options for refuelling it then. What I've done is put a fuel connector on a bit of pipe so I can refuel the inbuilt tank using the primer bulb.

<edit> Just looked at pic of your boat I think-is it the one from Scotland? If it is, make sure any aux you get can't hit the tubes with the prop.

Fishery Pokery · 13 February 2010, 10:41

Hi,
I have asked about aux's on my boat before and been told it wasn't a good idea by people with much more experiance than me. But it is always something that bothers me, especially as this year I will be going further afield with my new boat and unknown engine. I wouldn't want to rely on my rowing ability to get me to safety either.

I have a Tohatsu 9.8hp from a smaller sib I have, and I intend taking it out with me when I go out on my 4.5m sib. The boat currently has a 25hp engine on that I have been told is a good runner by the person who serviced it.

I have bought an outboard bag for the 9.8hp, and intend to strap it down securely. This would hopefully stay dry and not bounce about. I would carry two 12L fuel tanks as both engines are a 50:1 mix. The tanks will give me a good range, and prevent fuel problems.
If I encounter a problem when out, I can (hopefully) remove the 25 and fit the 9.8.
Also, when on holiday in Scotland, if one breaks down I am not scuppered for the holiday. I think the 9.8 will still shift the boat, just not warp speeds.

What do you think of this idea?
Also, when using a 25hp engine, does it have to be bolted to the transom? Obviously it would be tied to the transom, and secured with the thumb screws.
Cheers,
Geoff

Nos4r2 · 13 February 2010, 10:58

Quote:

Originally Posted by Geoff_Jubb

Hi,
I have asked about aux's on my boat before and been told it wasn't a good idea by people with much more experiance than me. But it is always something that bothers me, especially as this year I will be going further afield with my new boat and unknown engine. I wouldn't want to rely on my rowing ability to get me to safety either.

I have a Tohatsu 9.8hp from a smaller sib I have, and I intend taking it out with me when I go out on my 4.5m sib. The boat currently has a 25hp engine on that I have been told is a good runner by the person who serviced it.

I have bought an outboard bag for the 9.8hp, and intend to strap it down securely. This would hopefully stay dry and not bounce about. I would carry two 12L fuel tanks as both engines are a 50:1 mix. The tanks will give me a good range, and prevent fuel problems.
If I encounter a problem when out, I can (hopefully) remove the 25 and fit the 9.8.
Also, when on holiday in Scotland, if one breaks down I am not scuppered for the holiday. I think the 9.8 will still shift the boat, just not warp speeds.

What do you think of this idea?
Also, when using a 25hp engine, does it have to be bolted to the transom? Obviously it would be tied to the transom, and secured with the thumb screws.
Cheers,
Geoff

If you're set on it,I'd buy a 4hp as an aux. Sod's law says if your main engine breaks down, it'll be too rough to lift a 9.8hp onto the transom without losing it.
Ref bolting the 25 on,will you need to move it to one side to steer an aux properly?

Fishery Pokery · 13 February 2010, 11:27

I am keen on not buying another engine, unless I see one at a bargain price. Also I don't want to sell the Tohatsu 9.8hp as it is a good engine, and really light for its horse power (a two stroke).
I would have to remove the 25hp engine to use another. Both engines are two stroke, the 9.8 is light, the 25 has lifting handles on the side by the cowling. I often lift the 25 onto a bin to run it. I realise it would be a different kettle of fish on by boat, but do you think it is do-able?
Do you think the engine will get damaged strapped down?
And is the stress too much on thumbscrews alone, not bolts?
Thanks for taking the time Nos.

Nos4r2 · 13 February 2010, 11:43

Quote:

Originally Posted by Geoff_Jubb

I would have to remove the 25hp engine to use another. Both engines are two stroke, the 9.8 is light, the 25 has lifting handles on the side by the cowling. I often lift the 25 onto a bin to run it. I realise it would be a different kettle of fish on by boat, but do you think it is do-able?

No. Absolutely not.Forget taking the 9.8. You'll end up going in head first trying to lift the 25 off.

Quote:

Originally Posted by Geoff_Jubb

Do you think the engine will get damaged strapped down?

I suspect in a sib, it'ls more likely to come loose and very likely soaked.

Quote:

Originally Posted by Geoff_Jubb

And is the stress too much on thumbscrews alone, not bolts?
Thanks for taking the time Nos.

Nah, thumbscrews are fine as long as you do them up really tight, wiggle the engine about to see if they move/reseat then tighten them again.

spartacus · 13 February 2010, 20:45

Quote:

Originally Posted by Nos4r2

No. Absolutely not.Forget taking the 9.8. You'll end up going in head first trying to lift the 25 off.

Have to agree. It's one thing lifting a 25hp on the the slipway, quite another in anything other than a flat calm sea, especially if you're under pressure to switch engines.

Even if the 9.8hp was in a bag, it will rattle like a box of spanners. A Yamaha 4hp 2-stroke or Tohatsu 3.5hp would be better.

Paul E · 16 February 2010, 11:33

http://rib.net/forum/showthread.php?t=34311