44ft monohull with outboarders only

[castillino]

Are there any larger monohulls with outboarders only? I'd love to have everything related to the engine safely outside: easier to repair, could have two outboarders (backup), and even potentially use one for the dinghy.


Has anyone experience with such a setup?

[GordMay]

Greetings and welcome aboard the CF, Castillino.
An outboard engine, large enough to power a “larger” monohull [even as half of a pair], is going to be much too large to use on any conventional dinghy, and much too large to be practically portable.

[Benz]

What is your definition of "larger"?
I'd take outboard power up to 36 feet; beyond that, I think it would become impractical.
I have an OB on a 31' and it works fine.
An OB suitable for a big boat would not be so for a dinghy.

[JBP]

You can certainly get extremely powerful outboards today, I'm sure they could easily power a 44ft monohull. They are almost all gasoline, while there have been a few diesel outboards, they never became popular. The largest size generally considered "portable" is about 20HP which is reasonable for a large dighy. Even at that size you'll want a lift unless you are quite fit.

[Shanachie]

An outboard hanging off the stern cavitates in any sizeable waves, meaning the prop comes out of the water and races when it should be powering the boat.


Assuming maybe 50 hp outboard, you're talking storing 50 gallons or more of gasoline aboard. That's a lot of flammable, explodable liquid that would probably have to be stored in a permanent tank.


Also, outboards are a hell of a lot more finicky than diesels. There's a reason why most of the TowboatUS calls on the VHF are smaller powerboats. A diesel is more reliable and easier to work on.


A final note: A sure way to wreck the value of a large sailboat is to hang an outboard off the stern. That's a sure sign the boat has gone beyond the pale and is no longer worth repairing properly.

[Lee Jerry]

Originally Posted by Shanachie

An outboard hanging off the stern cavitates in any sizeable waves, meaning the prop comes out of the water and races when it should be powering the boat.

What you describe is actually ventilation.

Cavitation is when the water pressure falls below the vapor pressure and the water actually boils (when the prop is fully submerged). Damage can occur when these vapor cavities collapse releasing high energy, depending on where it happens.

[Munoz]

Here's an example of a 44 footer designed for twin outboards:

https://parker-marine.com/product/exuma-44/

Note that it is a light, easily driven design compared to most 44 footers

If you look up Atom voyages on YouTube, he has a recent video testing a Cape Dory 36 fitted with a 9.8hp tohatsu or a 6kw electric outboard.

The larger wharram cats often run 2x 25hp Yamaha high thrust outboards, and that's probably the set-up I would consider for a a large light or moderate dispacement (say 15 tons max) mono.

The critical thing is the diameter/surface area of the propellers, not the HP. You can move quite a big boat with a small high-thrust outboard (the seagull "barge-pusher" being an extreme example).

On the other hand I have seen both a 32ft mono and a 31ft prout cat that had been repowered with a standard 40hp 4 stroke outboard (ie proped for a dinghy or a panga) and neither owner appeared happy with the set-up

[castillino]

Thanks for the reply.

This reply of an owner with an OB converted boat absolutely resonates with me: https://youtu.be/zXdS0ufiu1I?t=424


I wish there were some larger boats with two OBs (one electric, one gas). The design the video show is a bit iffy as I think the motor bay can easily take on water, but it's nicely integrated into the boat.