Auxiliary ob advice for Antares 30 Fly ?

Lisa&Paul

Lisa&Paul

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Hi Our single engine Yanmar diesel seems reliable but as we are planning a few more adventurous trips from our base in North Cyprus to Turkey and Greek Islands in the coming year ( Covid permitting ) we are aware of the importance of a back up engine , our boat is 10.2 metres and weighs 6 tonnes , we are looking at a 2stroke Yamaha 9.9 hp brand new at a cost of 1,750 euro , probably a bit expensive but everything here is subject to a large import duty , plus side mooring fees and fuel are really cheap .

Appreciate any thoughts re power to weight ratio , suitability etc. bearing in mind it is a 'get home ' scenario in the event of main engine malfunction.

Regards Paul and Lisa
 
Go bigger than a 9.9 I had a 24ft Inboard Diesel boat with a 9.9 Evinrude 2 stroke mounted in the middle of the transom. I calm water non tidal I tried the outboard and at maximum revs it would not push the boat at more than 2.6 knots. Perhaps because of the big inboard diesel engine 4 blade propeller causing drag.
In hindsight as the 9'9 Evinrude is the same engine as the 15hp (2 stroke) but with a bigger carburettor I could have taken the HP up to 15hp but all the carburettor would have done was increase the engine revs.
In your case I would try and find an outboard with a bigger propeller Perhaps a twin cylinder with electric start
 
I usually argue you don’t need much for an auxiliary but in this case I gotta agree.

Plus you MUST go for a high thrust for this task. All a normal 25 HP will do is “bog down” as it tries to push a small amount of water at 25mph backwards where what you need is a large amount of water being pushed at 10mph so you need the special high thrust or sail power type engine so made specifically for slow heavy. Boat show - working boat so essentially.

And I think you need 25+ HP to make any headway at all at 6 tonne and that’s kind of size. A 2hp would do it on a lake with no wind, but you will have wind, waves and tides.... even then 4 or 5 knot will be all you will get
 
Most important of all, is how it’s mounted. If the lower unit and prop aren’t able to get below the line of the hull...it just won’t work at all. It will just suck a whirlpool of air from behind the transom. If it’s the boat I think it is. This means it needs to have a bracket on the bathing platform and then attached to that...a swivel lowering type bracket that’s able to get the engine low enough to work. Fine balance usually between the engine being low enough to work well...and being high enough not to drag in the water when underway with main engine and it tilted up. Needs lots of thought.
 
Ok , thanks for your replies which raise a few points ...... We generally sail in a calm area of the med with minimum tides and wind , so does this alter the engine size suggested to a degree ?

QBhoy ......Yes we get the need for a platform bracket and a swivel lowering bracket , when OB in situ what would you say is the ideal depth of water above the centre of the propeller to the surface to get max propulsion ?
 
The water needs to cover the cavitation plate by several inches, and if the boat pitches that can pull the stern up a lot.

You definately need long shaft.

As to the HP then it depends if you want it to push you towards destination, or just help keep you off rocks etc? If you are happy for it to work with tide and wind to give steerage it’ll help arrives, a 15 HP may suffice, but for any meaningful headway 25 HP would be absolute min - and in both cases as said b4 a high thrust option essential.

See :- Yamaha Outboards

Or

DF25A: 25 Horsepower Outboard Motor | Suzuki Marine UK Doesn’t explain the difference so well
 
Lisa&Paul said:
Ok , thanks for your replies which raise a few points ...... We generally sail in a calm area of the med with minimum tides and wind , so does this alter the engine size suggested to a degree ?

QBhoy ......Yes we get the need for a platform bracket and a swivel lowering bracket , when OB in situ what would you say is the ideal depth of water above the centre of the propeller to the surface to get max propulsion ?
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Hi. The AV plate that’s above the prop needs to be in line or close to the level of the lowest point of the hull, directly in front of the engine. Its not a given that you need a long shaft. Just depends on the range of travel you have with the bracket.
my boat has an auxiliary bracket that’s well enough positioned to allow a short shaft to be used. This means the engine also doesn’t drag in the water when on plane or going slow with the main engine. It’s a fine balance for sure.
I didn’t fit the bracket...but who ever did, got it spot on. It’s that well set up, that a 2.5hp on it will incredibly manage to push a 19/20ft boat along at 4mph at 3/4 throttle.
 
Yes, a light boat in calm water needs very little power to achieve low speeds - in fact the weight isn’t so much of an issue than the wind age. They used to move coal barges weighing thousands of tonnes with one single horse on canals....
 
Years ago I had a 24ft Hardy fishing boat with outdrive and the previous owner had added a 15hp Aux to the swim platform with remote controls. When I tested the set up before buying, the 15hp outboard did drive the boat forward without any problem and would appear to be a good idea - However, that test was done on a flat clam sea lock. When I tried it out in the North Sea, having got the boat home by road, the outboard could barely move the boat in any sort of chop and as waves got bigger (not storm just normal conditions) the outboard was coming out of the water as the boat pitched up and down. WOFTAM - (waste of flaming time and money) Removed and sold it.

Given that sod's law dictates you'll breakdown in deteriorating weather conditions -I'd have very little confidence of an outboard pushing your boat.
 
At 6 ton and aux it's not about hp because you cant make the hp and lay it down, but about torque. Your best bet would be a OB saildrive with high thrust prop but I doubt it will be effective. Yachts of similar size are running ~50 -90 hp diesels in them which is further reduced by the gearbox. If you were 2 ton and 28 foot it would be a potential solution but imo you are wasting your time.
 
Lisa&Paul said:
Hi Our single engine Yanmar diesel seems reliable but as we are planning a few more adventurous trips from our base in North Cyprus to Turkey and Greek Islands in the coming year ( Covid permitting ) we are aware of the importance of a back up engine , our boat is 10.2 metres and weighs 6 tonnes , we are looking at a 2stroke Yamaha 9.9 hp brand new at a cost of 1,750 euro , probably a bit expensive but everything here is subject to a large import duty , plus side mooring fees and fuel are really cheap .

Appreciate any thoughts re power to weight ratio , suitability etc. bearing in mind it is a 'get home ' scenario in the event of main engine malfunction.

Regards Paul and Lisa
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I’ve crossed the English Channel many times in a single engine boat.

Get a good anchor, a VHF, maintain your boat, have spare fuel filters and impellers (and know how to fit them) stop worrying and go boating.

It’s complicated and potentially ineffective ( I agree with Bruce) and anyway even if you make it work enough petrol to get you home introduces far more risk than you are eliminating.
 
robmchugh said:
Years ago I had a 24ft Hardy fishing boat with outdrive and the previous owner had added a 15hp Aux to the swim platform with remote controls. When I tested the set up before buying, the 15hp outboard did drive the boat forward without any problem and would appear to be a good idea - However, that test was done on a flat clam sea lock. When I tried it out in the North Sea, having got the boat home by road, the outboard could barely move the boat in any sort of chop and as waves got bigger (not storm just normal conditions) the outboard was coming out of the water as the boat pitched up and down. WOFTAM - (waste of flaming time and money) Removed and sold it.

Given that sod's law dictates you'll breakdown in deteriorating weather conditions -I'd have very little confidence of an outboard pushing your boat.
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Typical example of why it needs to be set up properly. Very tiny measures and tolerance in it to get it right.
 
This is something I have thought about often and perhaps the forum knows the answer;
Rather than put an auxiliary motor on the boat, would it be more efficient to have a large outboard on an oversized tender and just tow the mothership?
 
Bouba said:
This is something I have thought about often and perhaps the forum knows the answer;
Rather than put an auxiliary motor on the boat, would it be more efficient to have a large outboard on an oversized tender and just tow the mothership?
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Doesnt really work. In the battle of friction the boat wins hands down. When I've tried the tender just skips sideways and is almost impossible to steer, literally. You can have the tender hard to port while skipping to starboard. If you tether the tender to the boat you lose steering and worse off than just placing it at the back of the boat. The lighter the boat the less this effect but on six ton vs 150kg? Na, you're dreaming. Pull, barely, control, nada
 
Bouba said:
This is something I have thought about often and perhaps the forum knows the answer;
Rather than put an auxiliary motor on the boat, would it be more efficient to have a large outboard on an oversized tender and just tow the mothership?
Click to expand...
Or have the larger OB for the tender that can double as an aux engine for the mothership?
Seen that done on a 30ft (ish) Sealine, the OB was on a swing bracket on the swim platform* but also used on the inflatable zodiac

*Or transom
 
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Elessar said:
describe how to set it up properly then
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I did early on. Have a look. But in some cases when weather is really bad and on a boat like a Hardy, that will naturally roll and pitch quite easily. Might not make too much headway in those conditions !
 
QBhoy said:
I did early on. Have a look. But in some cases when weather is really bad and on a boat like a Hardy, that will naturally roll and pitch quite easily. Might not make too much headway in those conditions !
Click to expand...

I think your perception is skewed due to the size of your boat. I wholeheartedly agree with you though. In your circumstances it is not only viable but practical. I've done it myself and have posted videos here of it. Then you come to a boat 6 times heavier than yours. You stand on the pontoon and give it a gentle shove. It moves almost effortlessly away from you. You think to yourself damn that was easy my 2hp would make light work of this. But trust me I have tried. I experimented for the hell of it. At anchor I have pulled mates that were about to ground stern ashore when the wind changed and they have their drives up or dare not start the engines when on shafts. I have tried to move boats for a kedge anchor into the swell instead of wind. Many, many times. Trust me, it's simply not a viable solution. Arguing the toss is a comfort factor, not pragmatic.

edit: this was done on dinks with 8 and 10hp 2 stroke twin cylinder OB. Every stroke one piston is firing, re torque and continuity
edit2: on a 15hp I couldnt lay the hp down. At above half throttle the prop just ventilated, the motor screamed and any push went pffft.
 
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