Dingy Outboards - long shaft vs short

[TPG]

I have a general question about dingy outboards when it comes to shaft length choices. Seems that most short shafts are around 15" and long are around 20" approx.

All things being equal, what are the advantages/disadvantages between the 2?

One point that I'd read said that a long shaft had the advantage of being more flexible when motoring with the leg in an upward position when navigating very shallow water.

Would like to know your experiences.

[thomm225]

You pick long or short shaft based on transom length whether it's on a dinghy or a small power boat.

If you put a long shaft on a transom that should have had a short shaft, the vessel will not plane properly

Found this example on Youtube.

https://www.youtube.com/watch?v=crjAmltyeW4

[rslifkin]

It's not a question of one being better, but a question of which one fits the specific dinghy in question. Which one you need to put the anti ventilation plate and the prop at the right height is dependent on the height of the dinghy transom. Many will need a short shaft, but some larger dinghies will have taller transoms that need a long shaft.

[capn_billl]

The only advantage I can see of getting a long shaft for a typical RIB dinghy would be if you had a smaller sailboat, and wanted to use the outboard as a backup for the mothership.

A 20 HP long shaft will power the dinghy just fine, and will also move a 30ft sailboat on an adjustable outboard bracket just fine.

[Ifitsworthdoing]

Following, and for the reason capn_billl mentions - although in my case it will be an electric outboard with a max. RPM of 1440 rather than the 5000 typical of petrol motors which I reckon may substantially reduce the welling up of wake and associated water ingress …

[Stu Jackson]

To add: dinghies go into shallow water, hence a less deep prop is desirable.

[Bay Breeze]

Originally Posted by capn_billl

The only advantage I can see of getting a long shaft for a typical RIB dinghy would be if you had a smaller sailboat, and wanted to use the outboard as a backup for the mothership.

A 20 HP long shaft will power the dinghy just fine, and will also move a 30ft sailboat on an adjustable outboard bracket just fine.

Exactly. We use as long shaft Torqeedo to get our Pearson Ensign from the dock to a place we can sail. Then use it on our RIB when cruising. The daysailer needs the long shaft. Not so with the inflatable dingy. Not perfect but a two-fer.

[chris mac]

Here in the Bahamas, a short shaft (provided it submerges enough to work) is best. There is a lot of shallow water and sandbars that a long shaft will not get into

[MJH]

Originally Posted by TPG

I have a general question about dingy outboards when it comes to shaft length choices. Seems that most short shafts are around 15" and long are around 20" approx.

All things being equal, what are the advantages/disadvantages between the 2?

One point that I'd read said that a long shaft had the advantage of being more flexible when motoring with the leg in an upward position when navigating very shallow water.

Would like to know your experiences.

While it would be wise to always check on the depth of the dinghy's transom before purchase, generally speaking the long shaft outboards are usually for smaller sailboats.

~ ~ _/) ~ ~ MJH

[MicHughV]

I have no scientific data to back this up....but after almost 40 years afloat, I've never seen a long shaft on a dink, not ever.....nor can think of a single reason to have a long shaft...most modern day dinks get up on plane, and they move at speed. A long shaft would simply provide more water resistance and slow the dink down.

The longer shaft also puts more of a "lever arm" force on the dink, exactly what you don't want...

As for shallow water dink operation, most small dinks have a lever on the side of the engine allowing for a tilt up operation.....this is probably standard on all small engines...meaning your long shaft in tilt up mode will likely be the same as your short shaft in normal mode.

[rslifkin]

Originally Posted by MicHughV

I have no scientific data to back this up....but after almost 40 years afloat, I've never seen a long shaft on a dink, not ever.....nor can think of a single reason to have a long shaft...most modern day dinks get up on plane, and they move at speed. A long shaft would simply provide more water resistance and slow the dink down.

Most of the stuff that would use a long shaft is a little bigger than what most carry for dinks, that's why. You're typically in the 14 - 16 foot range before you see transoms tall enough to call for a long shaft. And most of us just can't carry a dink that big.

[MicHughV]

I run a fishing a boat as well...I'm at a marina where there must be 100's of fishing boats as well, every make, length and description...not one has a long shaft engine....not one...
The long shaft is really only suited for those applications, where the engine is mounted on a moveable engine bracket...something you might see on the transom of a 20 something footer sailboat.
This keeps the engine out of the water, but the prop deep enuff, so that small waves don't lift the prop clear of the water.
I can see no other situation, where a long shaft would be appropriate.

[poiu]

You get the shaft to suit the dinghy’s transom depth.

I’ve got a short shaft dinghy. It’s disappointing. I used to have a long shaft dinghy. It had a much more comfortable ride. Short shaft dinghies have flatter bottoms and smack the waves instead of cut through them.

Most small dinghies are only available in short shaft. In between you can get both, but the ones with two options will be flat, but with a raised transom on the long shaft model.

[rslifkin]

Originally Posted by poiu

You get the shaft to suit the dinghy’s transom depth.

I’ve got a short shaft dinghy. It’s disappointing. I used to have a long shaft dinghy. It had a much more comfortable ride. Short shaft dinghies have flatter bottoms and smack the waves instead of cut through them.

Most small dinghies are only available in short shaft. In between you can get both, but the ones with two options will be flat, but with a raised transom on the long shaft model.

In the small sizes they tend toward flatter bottoms for better planing with small engines. The tradeoff is a worse ride, but it avoids building a dinghy that won't plane fully loaded with the biggest engine it's legally allowed to carry.

[flyingfin]

Short shaft, limited market for resale
Long shaft, most used as it is functional for dinghys, john boats, skiffs
X-long shaft, sailboat kicker