Auxiliary outboard for 21ft cuddy

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mikehibb

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Hello All,

I am looking for some advice regarding auxiliary outboard for a 21ft cuddy, the boat is in the med/aegean, no tide to worry about. Use is bay hopping, never venture more than a couple of miles from land etc when visiting nearby islands.
Current engine is a new Etec 115 which we are very happy with but this season our young daughter will be coming aboard hopefully so we wanted an emergency get us back to shore type back up.
As the boat is out of EU, we can still pick up a Tohatsu 2 stroke, so we were thinking that the 8hp or 9.8hp might be around the right size. note the boat is only 1200kg (including engine and a full tank) We only need to make 4 or 5 knots and we would never be more than half an hour from shore on the aux.
Thanks in advance.

Mike

(ps new to this side, sold the raggy last year)
 
Hi Mike, the 8 will probably do, once you are at 10hp, the weight is the same as the 15hp, so you may as well fit the bigger hp. The two stroke will suit the application, cheaper, lighter and better suited to occasional usage, less servicing costs than the four stroke, generally.
Make sure it's a long shaft, to keep the prop in the water while the boat is pitching (fore-aft motion). Keep checking the auxiliary bracket bolts every season or two, they can work loose if the boat bounces around in heavy seas.
There is a model of Mercury two stroke with a "Co-Pilot" lever, locking the outboard steady, from swivelling, so you can steer the boat from the main helm once you set the throttle. A lot more civilised than leaning over the stern.

Good luck

Edit: drain the fuel from the carb after each run by disconnecting the supply hose or shutting off the valve (which ever is applicable) until the engine stops. This reduces the oil residue (once the petrol evaporates) collecting in the carb and potentially creating blockages in the future.
Lift the cowling from the power head, a couple of times per season, and give the whole engine a liberal spray with a lanolin based spray to protect it from salt spray corrosion.
 
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AndieMac said:
Hi Mike, the 8 will probably do, once you are at 10hp, the weight is the same as the 15hp, so you may as well fit the bigger hp.
Click to expand...

Actually with the Tohatsu 2 strokes, the 10 is the same block as the 8, so that's the way to go. On a light boat, with no tides to worry about and short distances to travel, I think it'll do the job nicely.

A 2 stroke is a bit more hassle in this case because you can't just make up an adaptor for the fuel line and swap it over if the main engine conks out, but it's not that difficult to work out a way to pre-mix the fuel when the need arises.
 
Nick_H said:
A 2 stroke is a bit more hassle in this case because you can't just make up an adaptor for the fuel line and swap it over if the main engine conks out, but it's not that difficult to work out a way to pre-mix the fuel when the need arises.
Click to expand...

Hi Nick,
A service guy told me that most issues relating to main engine (outboard) failure was fuel related. So having a reserve supply of premix in a smaller tank could be an option. Not always convenient in a 21 foot boat to find the space, but say 10 litres would get you a fair way at moderate revs.
At the end of the season the left over fuel can be used in either garden equipment or heavy diluted back into a car.

I carry an oil extraction pump (and extra two stroke oil) to draw extra fuel from the main tank (a direct access cap) if the main engine failed due to a mechanical problems, to top up the auxiliary tank.
 
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Agree that the Tohatsu 9.8 is an excellent choice.

If at all possible try and get a "Saildrive" or "High Thrust" propeller fitted. If you can't, then get the largest diameter, lowest pitch prop (perhaps 4 blade) you can.

The 9.8 Tohatsu comes with a propeller designed to run a RIB or tender at planing speeds. Because this engine won't get your 21' boat to planing speed it's like trying to drive your car everywhere in top gear. The engine won't pull max rev's or run as well as it would with the correct prop.

If such a thing exists, try and get the Sail version of the 9.8 - something like this here....

http://www.selvamarine.co.uk/product.php?line=mot_4t&prod=blackbassbigfoot-8

http://yamahaoutboards.com/outboards/High-Thrust/overview - more info here and http://yamahaoutboards.com/outboards/High-Thrust/benefits here

https://www.mercurymarine.com/en/us/engines/outboard/fourstroke/8-99-hp/ Also here - they call it the Command Thrust

Can't find a 9.8 Sail drive on their site - but then they don't list a 9.8 two stroke over here either - this is closest http://www.tohatsu.co.uk/tohatsu-mfs6-sailpro.htm


When I had a 28 footer we tried loads of outboards, and a 6hp saildrive produced the same speed (bar about 0.5 of a knot) as a 30hp standard outboard!!!

Basically the 30hp never got over about half speed as it's prop was trying to push water fast whereas the saildrive was trying to push water more slowly and at higher volumes - which was better.
 
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Many thanks all for your help.
It looks like the Tohatsu 9.8 is the one to go for, which is what I had pretty much guessed earlier.
I have had 2 stroke Tohatsus before so I am familiar with the draining the carb etc, also our local gardeners are more than willing to take end of season fuel.
I will also investigate the sail drive/high thrust prop version too.

Again
Thanks all

Mike
 
Regarding sail drive higher hp etc etc. I have a 21 foot cuddy too. Her displacement speed is 5 knts. A dinky little 3.5 hp on my tender pushed her at 5 knts. My own aux 8hp 2stroke will only push her 5 knts. A 15 hp engine will only push her 5 knts. You see where I'm going here right? Get the lightest most reliable aux you can afford or twin engine. Lightest because my 8 hp still weighs in at 30 plus kg but the 3.5 is feather light although I wouldn't vouch for the 3.5 in a headwind.
 
Thanks for your info too Bruce, especially on the smaller powered engines.

This is now especially relevant as it looks like I need an alternative plan as just today I found out that Turkey has adopted basically the same emissions regs as EU did a couple of years ago, and now they can only sell existing stock and no new 2 strokes ( well the smaller ones not the etc types obviously as they meet the emissions)

My local contact has just had a run on their existing stock and sold out of all the 2 stroke Tohatsus.

So based on a similar weight to the 9,8 2 stroke the nearest option is a 6 hp 4 stroke.( in at 25kg). Tohatsu do a sail pro high thrust version of this, but I would prefer a normal long shaft but with the same sail drive high thrust prop which I can buy separately.
Standard props of the 6 hp 4 stroke are as follows ( hope I format it ok)
dia pitch blade
ALUMINIUM LIGHT 7.9 9 3 369B645181
ALUMINIUM MODERATE 7.7 8 3 Y (non-Sail Pro models) 3R1B645161
ALUMINIUM HEAVY 7.7 7 3 3R1B645141
ALUMINIUM HEAVY 8.375 6 3 Y (Sail Pro models) 399B645121 HIGH THRUST
ALUMINIUM HEAVY 7.9 6 3 393B645121

Light=100-500lb
Medium = 500-1500lb
Heavy=1500-3000lb ( where I would fall in to)

As I mentioned in the first post just looking for 4 or 5 knots in non tidal area, mainly bay hopping just need an emergency engine get to shore/safe haven to drop wife and daughter on beach, I do not mind a couple of hours trundle back to base. In our area there is a beach cafe/jetty in nearly every bay, three marinas and at least 8 local fishermens harbours around the Bodrum peninsula ( only 50 kms long itself) so not far to go.

So hoping that the 6 hp high thrust will be ok.

Thanks again in advance.
MIke
 
BruceK said:
Regarding sail drive higher hp etc etc. I have a 21 foot cuddy too. Her displacement speed is 5 knts. A dinky little 3.5 hp on my tender pushed her at 5 knts. My own aux 8hp 2stroke will only push her 5 knts. A 15 hp engine will only push her 5 knts. You see where I'm going here right? Get the lightest most reliable aux you can afford or twin engine. Lightest because my 8 hp still weighs in at 30 plus kg but the 3.5 is feather light although I wouldn't vouch for the 3.5 in a headwind.
Click to expand...

Whilst you're right in this - you hit the nail on the head at the end.... A 3.5 would push it pretty much to hull speed on a sheltered lake, but get a hefty headwind and it would have no chance....
 
Many thanks again Bruce.

Looks like I will be OK with the 6 and a high thrust prop. Your video showed me exactly what I was looking for.
Regards
Mike
 
Took longer to get fitted tan expected, due to a week long festival over here in Turkey.
Any way took less than an hour to get the bracket fixed and outboard on yesterday. Beached the boat to do it. The fun was getting back off the beach ( lee shored) in a 4 gusting 5.
Luckily with a good shove back from my fitter we managed to get the main outboard down enough for some reverse thrust.

It has been blowing a hooley ever since, so hoping for some calmer weather to break in the motor. Will report back later.
 
Well finally managed to give the aux a bit of a run today.

As I mentioned above, we ended up with a 6hp 4 stroke, long shaft ( standard prop at the moment)
Pretty calm day today, and managed an easy 8 kmh ( must change the settings on the GPS) at half throttle. Did not want to rev any higher as it is still being run in.

So we still have some spare hp for slightly heavier seas, will also change the prop next year for a sail drive prop.

Many thanks all.
 
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