Which outboard for emergency backup?

[Jammer]

1) If in doubt as to whether you have sufficient diesel, carry extra diesel, not an extra engine. If in doubt about the cleanliness of the diesel tank, clean it. If in doubt about microbial contamination, use a biocide. A diesel auxiliary is a great setup and in most cases more useful and reliable than an outboard. Treasure what you have, the grass is not always greener on the other side of the fence.

2) The best way to move a larger boat with the dinghy outboard is by hip towing it with the dingy engine on the dinghy. A quick google search will turn up articles on how to do this.

3) I have had 25'-ish sailboat with small outboards, two of them. You want a high thrust motor with an extra long shaft. High thrust motors with extra long shafts make terrible dinghy outboards because the prop is pitched wrong and the extra long shaft makes the dinghy unstable in turns and hard to plane on the straight.

4) Give some thought to gasoline tankage and safety as part of your installation.

5) If you really want a straight answer to your question rather than to be talked out of it, your best bet is to use the Tohatsu 3.5 you already have, which will sort of move the boat (4 kts probably) in benign conditions (no wind or current). Any bracket that gets it in the water with the cav plate just below the surface of the water and the prop mostly below the bottom of the hull will sort of work. Control and steering access, as pointed out upthread, is a thing to consider. If you want a motor that is truly sufficient for a boat that size in a wide range of conditions you will need a 10 hp high thrust. I had the Yamaha one in 8hp which is essentially identical, they're good for that. I would lock the steering and use remote throttle/shift controls, plus the rudder.

[Don C L]

I agree with Statistical, and my auxiliary is an outboard. Get the diesel right and then use the dinghy if needed.

[thomm225]

You don't have to keep the outboard on the bracket.

Just put it there, when you need it.

Keep it stored away when not needed.

A short shaft dinghy outboard will work when near your slip.

Offshore, you'll have to sail in then use the dinghy short shaft outboard to get to your slip.

Sometimes when it's rough I can't use my outboard offshore so sail in to the creek then use it.

Most times if it's rough, the wind is up so you can sail.

It's been my method for the past 13 years.

One time my outboard over heated due to a disintegrated impeller.

It wouldn't start until it cooled. So I sailed up close to my slip, removed the outboard's cover, started it, and motored to my slip.

[CarlF]

As others have said, a short shaft dinghy outboard is a terrible choice. You have to get the bracket so close to the water that controlling the outboard is difficult. And it will cavitate into a useless eggbeater in any wake or wave. You need a long shaft and a low pitch propeller.

But your dinghy will make a fine push boat. Tie it at the stern quarter beside the boat. With a little experimentation you will figure exactly where to put the lines.

And fix you fuel system! A reliable diesel beats an outboard every day of the week. 1) Upgrade to a good filter like the Racor 500. These filters take a long time to clog, the elements are inexpensive, and they do a good job at seperating water out. 2) clean the tank. All old tanks need occasional cleaning. Many marinas know of a professional tank cleaning company. This is the best way as they have special equipment. 3) Replace the o ring on your fuel fill cap. This $2 fix stops rain leaking in the fill - the most common source of water which causes the bug to grow.4) Install a vacuum filter so you get early warning if a filter clog. 5) And finally add a little biocide whenever you add fuel. One good plan is to alternate Startron and biobar JF as they work better on different bugs.