Ok to use a long shaft o/b with my dinghy?

[herdman]

I have a LONG SHAFT 6hp suzuki 4 stroke for a drascombe lugger - would it be ok to use it with a pretty stable 3.2 metre dinghy for a few weeks? or will the handling be all over the place? any one tried this?
thx for any advice...

 

[seumask]

Should be fine if you are cautious.

 

[sarabande]

if the plate on the dinghy says 6hp is OK, then yes, but on accelerating you may bring the nose up a bit and dump everyone at the stern, which lifts the nose even more, which...

Been there once.

used sensibly, should be OK.

 

[herdman]

thanks for this - actually dinghy rated to 10hp - actually maybe its about 3.6 metres - cant remember but its v stable with big tubes..

 

[Leighb]

One possible problem might be difficulty starting? Certainly on a Seagull if the exhaust is too deeply immersed it is difficult/impossible to start.

 

[Ecosse120]

The only other issue you may have is that the exhaust could be too low in the water and you may have an increase in back pressure, which causes the engine to stop. Best bet is give it a go.

 

[Tranona]

Outboards are specifically made to fit transom heights. A long shaft as its name implies is made with a longer shaft for a higher transom such as on a small yacht.

Most tenders have lower transoms and therefore use standard (or short) shaft motors. Your Long shaft is not suitable for a tender - irrespective of HP - because the prop will be far too deep in the water. Not only will this result in an increase in draft of 6 inches or so, but you will experience starting and running problems because the exhaust is too deeply immersed.

 

[cliffordpope]

I use a long shaft Seagul in a small dinghy. It just needs a collar clamped on the tube so the outboard sits higher and the bottom end is at the correct depth. It works perfectly.

 

[VicS]

would it be ok to use it with a pretty stable 3.2 metre dinghy for a few weeks? or will the handling be all over the place? any one tried this?

Try it is the sure way to find out.

No problem apparently with the power nor presumably with the weight.

Depth of immersion of the exhaust outlet may cause starting difficulties .. but it probably depends on how generously sized the relief ports are.

Increased draught will need to be watched or you'll keep bashing it on the beach, slip, hard or whatever.

Increased drag I guess is not going to be aworry.

You could consider bolting a decent bit of timber onto the transom to make a mounting about 5" higher than the normal transom top.

 

[tcm]

I think that there's the possibility that using a slightly-longer shaft outboard risks all sorts of dangers including flipping over the dinghy, going into orbit and death.

Even moderate-sized sense of adventure - missing on a lot of boats it seems. Heyho.

 

[Tranona]

I use a long shaft Seagul in a small dinghy. It just needs a collar clamped on the tube so the outboard sits higher and the bottom end is at the correct depth. It works perfectly.

Seagulls are/were made in 3 shaft sizes The 40 Minus or Featherweight is 13" and made specifically for small inflatables with very low freeboard. Otherwise, Standard shaft length is 15" - same as other standard sizes for dinghies. There was a collar avaialble for the shaft casing that was 2" wide to raise the power head of the 40 Plus to give (surprise surprise) 13" shaft length when using on low freeboard dinghies such as the Redcrest. Immersion of the exhaust influences starting because of back pressure in the exhaust.

Long Shaft (21" - again industry standard) were available as alternatives on 40 Plus and Silver Century models where these engines were used on boats such as day sailers, small cabin yachts and larger dinghies with higher transoms or outboard brackets. The collars can also be used on these models to fine tune depth for non standard transom heights.

I remember introducing basic diagrams into the publicity material and handbooks to communicate these basic facts to users when I was responsible for "Marketing" at Seagull in the 1970's.

 

[NorthUp]

I used a 5 HP longshaft Mariner on a 2.8m dinghy for a year without any problems.
Its a bit slower, and the 'brakes' worked well when you shut the throttle.
I had a longshaft, as it doubled as a standby engine for a RIB.

 

[VicS]

There was a collar avaialble

What bit like this

 

[OGITD]

Should be fun!

I've had my Yam 6hp 2~ long shaft (detuned 8) on the back of a 2.9m and had hours of fun….so this should be no problem as long as you know how to control an inflatable.
Too many people use reverse to try & stop, or try to just fend-off when good throttle control and directional thrust is what you should use to control speed, direction and stability.

 

[Tranona]

What bit like this

Yes, cunning piece of engineering. Actually each half of the clamp is the same as the friction side of the main clamp. Two bits of Bakelite plus two bronze bolts, nuts and washers and you have a spacer! In theory could be clamped anywhere on the shaft to vary shaft length, but using it to turn a long shaft into a short shaft results in top heavy motor!

Happy days!

 

[Mark-1]

Holy thread revival batman.

For two seasons I've used two long shafts on a dinghy (Mariner 5hp 2T and Tohatsu 3.3hp 2T) without any issues whatsoever.

The thing that does concern me is the extra leverage + high thrust prop effectively twisting the transom and ultimately damaging it.

Has anyone ripped the transom off a dinghy with sheer revs? If anyone wants to donate a dinghy I have a 6yo lad eager to try.

 

[Graham376]

My original T9.8 was a long shaft .The engine started and ran fine on the dinghy but handling and (obviously) beaching not good so converted to short shaft with second hand leg.

 

[Boathook]

Holy thread revival batman.

For two seasons I've used two long shafts on a dinghy (Mariner 5hp 2T and Tohatsu 3.3hp 2T) without any issues whatsoever.

The thing that does concern me is the extra leverage + high thrust prop effectively twisting the transom and ultimately damaging it.

Has anyone ripped the transom off a dinghy with sheer revs? If anyone wants to donate a dinghy I have a 6yo lad eager to try.

If you get a dinghy let us know how your son gets on ! Or better still use existing dinghy ...

 

[CAPTAIN FANTASTIC]

The difference between short and long shaft is relative small. Its perfectly ok to use a long shaft outboard on a inflatable dinghy and you will not be able to tell the difference; i have done it for years.

 

[Tranona]

The difference between short and long shaft is relative small. Its perfectly ok to use a long shaft outboard on a inflatable dinghy and you will not be able to tell the difference; i have done it for years.

Do you call 6" difference "small. Why do you think motors are made to suit particular height transoms if it does not make a difference. Of course it is possible to use the wring length, but if you read all the comments above you will see that most people find a long shaft on a dinghy unsatisfactory for a variety of reasons. OK if you are seeking the rare compromise of one motor to do 2 different boats, but for a dedicated dinghy motor best to get the right one for the job.