Auxiliary Power with Outboard

[LettaD]

Have a 30’ O’Day with an inboard diesel and would like to add an outboard engine just as secondary power in an emergency.

She’s a very heavy (12,000) boat and I am wondering if anyone has done this and what size outboard would work?

Letta

[carlosproa]

30 ft is considered a light boat, you can even make a Yuloh and just paddle away slow and steady.
I had a Charlie Morgan 1972 that I fitted an auxiliary 4 HP engine on a titling bracket. It worked fine given the sea conditions I chose to use it when the Atomic 4 went caput.
That was a long time ago in an area and era when services like Boat US towing was not available. You can always sail to your destination and anchor to wait for favorable tides, wind, sea state. Once is calm a small HP engine will do the job

[LettaD]

Would a 20 hp long shaft stop her on a dime if I had to maneuver her into a slip around $1 million dollar boats?

Letta

[MicHughV]

The outboard will only work if the prop is in the water....you will likely need an "extension" fitted to whatever outboard you chose to get it deep enough, but even then, wave motion, will lift the prop out of the water..I know, because I've tried it...it can work in smooth water, but that is about it. Likewise, with the engine down, the cowling will be at or near the water, and it won't take but one errant wave to knock it lose. a 15 hp can give you all the power you'll need, but it's a heavy engine, not sure if any of the foldable outboard brackets can handle a 15. A smaller engine would likely also do the job, depends on what you'll use it for.
Lastly outboards suck a lot of fuel, given that you standard carry on fuel tank is only about 6 gallons, you will need to plan on how you are going to keep it filled.

[MicHughV]

outboards have notorious poor reverse..

[cr180]

Originally Posted by LettaD

Would a 20 hp long shaft stop her on a dime if I had to maneuver her into a slip around $1 million dollar boats?

Letta

We had a Cal 25 powered by a 10 hp outboard. More than enough power. Would think an outboard would be fine for your Oday 30. Would need an onboard motor bracket on transom. The issue though is shaft length. A long shaft is 20”, most outboards for sailboat propulsion mounted on transom brackets are 25”. A 20” may work in flat water but may not in a rough sea.

[deblen]

A friend & I brought his Southern Cross 28 over 50 nm up the Maine coast using his 11ft Avon with Honda 5hp. We maintained near 6kt/hr easily without running the outboard hard.
We used a hip tow with the dinghy stern & o/board sticking out behind the transom by approx. 2 ft.-for steerability.
We learned that we could lock the swivel steering knob on the Honda dead ahead & steer the boat from tiller helm in the normal manner.
This meant that the dinghy man (me) could stay aboard the mother ship most of the time.
The trip was nearly as comfy as if the A4 was pushing.
Since I usually tow a dinghy on most trips,I personally, would not bother with a separately mounted outboard.
YMMV
Cheers/Len

https://www.youtube.com/watch?v=TGVWWCE_q0M

[Jammer]

Originally Posted by LettaD

Have a 30’ O’Day with an inboard diesel and would like to add an outboard engine just as secondary power in an emergency.

She’s a very heavy (12,000) boat and I am wondering if anyone has done this and what size outboard would work?

Letta

I have a 26' Hunter that is 5,000 pounds. I have a Yamaha 8 hp high-thrust that is WAY more thrust than I need. A Yamaha 9.9 high-thrust is available and would be just right for your situation.

[Jammer]

Originally Posted by LettaD

Would a 20 hp long shaft stop her on a dime if I had to maneuver her into a slip around $1 million dollar boats?

Letta

That's huge, don't do it.


The Yamaha 9.9 high thrust engines are available in short, long, and extra long shafts. If you use a fixed bracket you probably want the extra long. If you use a bracket that slides up and down or pivots up and down then you probably want the long. With the movable bracket you get the outboard completely out of the water when at a slip or sailing but it is harder to reach the controls.

[Jammer]

Originally Posted by MicHughV

The outboard will only work if the prop is in the water....you will likely need an "extension" fitted to whatever outboard you chose to get it deep enough

Not my experience, I have a Yamaha 8 hp extra long (25") shaft, works great in seas up to 3'.

Lastly outboards suck a lot of fuel, given that you standard carry on fuel tank is only about 6 gallons, you will need to plan on how you are going to keep it filled.

Modern 4-stroke outboards use 0.1 gallon per horsepower per hour. So for a 9.9 hp outboard with the throttle wide open that's basically 1 gallon per hour. You can get portable outboard fuel tanks in your choice of 3, 6, 9, or 12 gallon depending on what you need. I have two 6 gallon tanks but ordinarily only carry one on the boat unless I am on a river trip or something where I'm going to be motoring all day.

[Greg Mason]

I thought you meant auxiliary power. I was thinking an outboard with a rectifier to make 12v in case. I believe you would need a 9.9 at east for that.

[bjp447]

I used a 5hp on a 29 foot Soverell
Worked fine
Sailboats don't backup well , outboards or not

[chasfgr]

Originally Posted by MicHughV

outboards have notorious poor reverse..

Probably because most don't realise that the gearing is much lower.
The troubles with a transom mounted outboard are manifold, only to be used by the experienced in relatively calm conditions.
My first boat had a 15hp Johnson, on the back - I found that a 2 hp did nearly the same job with far less hassle.
Anticipation is the name of the game.

[FabioC]

Has anybody implemented (or at least studied) something like this on a larger boat (say a high-freeboard 35')?

In principle, this could be an extra peace of mind... on many boats, we store the dinghy's outboard on the stern rail anyway, so if somehow some sort of bracket could be devised to be able to lower the outboard to the water... the intended use would be only in case of an emergency (say, losing main engine power just windward of a rock, or something like that), and just to get you to safety to give time until you can raise sails, or drop anchor, or whatever...

In practice, it may not be feasible on a 35' or similar. For one thing, the dinghy's outboard is often short shaft (I guess a long shaft could be made to work on the dinghy, but an extra-long shaft is very doubtful to say the least), so the bracket would have to be very long, and the controls may become unreachable once the outboard is lowered...

Or it may not work all together for other reasons (not enough power, the outboard would have to be off-center not to interfere with the swim platform, or other considerations)... I have considered something like this, but never spent the time to understand if it is feasible or not on a larger boat, so if somebody has studied this, it would be very interesting to know.

[Scubaseas]

Originally Posted by Jammer

I have a 26' Hunter that is 5,000 pounds. I have a Yamaha 8 hp high-thrust that is WAY more thrust than I need. A Yamaha 9.9 high-thrust is available and would be just right for your situation.

This. High Thrust is what you want. 20HP is way overkill. Reverse is "meh" but if you can habe someone steer it would be like having a stern thruster.