outboard madness!! long or short shaft?

[worstfirstmate]

Hi everyone!
I've been having an internal debate about which outboard to run on my dinghy and which to sell.

I have a 4hp Evinrude from the 1970's (short shaft) that I plan to use; but on the other hand i have a 1990's long shaft 6hp yamaha.

my dinghy is rated for up to 8hp, but I worry the long shaft will be a headache for my small dinghy?

the advantage to the 6hp longshaft would be I could use it as a backup motor for my 27 foot vega, which currently has a 9.9 johnson longshaft.

what do you all think? thanks in advance!

[GreenWave]

Most dinghy's are not going to work well with a long shaft outboard of any HP. You will either be lifting it part way up frequently if in shallows or you will be putting more pressure on the transom than desired due to the sub-optimal drive angle. Given you have two relatively small HP engines I suspect the long shaft will be a mistake due to dinghy size.

[rslifkin]

Measure the transom height of the dinghy. That'll tell you whether the short or long shaft will be a better fit on the dinghy. If the transom isn't tall enough to use a long shaft, then the long shaft will perform poorly and likely won't be any faster than the lower powered short shaft.

[Jammer]

What kind of dinghy? Is the transom designed for a long shaft motor? If not, can you modify it to add height? Typical RIBs use short shaft motors and are hard to modify.


Using a long shaft motor on a dinghy designed for a short shaft motor, can give you problems with the bow riding high resulting in squirrely steering and possible loss of control, in addition to excessive draft and too much torque on the transom.


Some hard dinghies are designed for long shaft motors, with a higher transom, which works out great because you have more freeboard on the transom and are less likely to get swamped by a wave or from a heavy load in the stern.

[sail sfbay]

Short shaft for a dinghy.

[PhilC]

If your dinghy is rated for 8hp short (16") a 6hp long (20") should not exceed the transom capacity (if it's in good condition - if it's a PVC boat with a glued in transom stick with the 4hp). Extending the transom for a small outboard like that is just bolting some alloy plate with a plywood packer to the existing transom.

[Ballsnall]

The long shaft will be fine on you dingy, it's only 6hp and it does double duty as your ancillary motor.
Sometimes you can add a bit of height to the transom to help. If you use the dingy in shallows a lot then maybe sell both and buy a newer short shaft 8hp.

[crashley]

Bolt a board onto the dingy to raise the outboard and then use the long shaft