which shaft do i use ??? Long or x/long

[sportfish550]

Hi guys sorry to bother everyone again , but i am thinking of upgrading my out board & at the moment i have a longshaft fitted to it, but i think a xtra longshaft would fit better. Would anyone know if i could use a 25inch instead of the 20inch ???

Boat: 550 sportsfish
Transom height: from top of mount bracket to keel is 21.5 inches

If someone has a sportsfish can they please tell me the best length to use.

[shonky1]

With my Sport Fish I use a 25 inch, with the shorter legs they tend to cavitate and wash out.

[Noelm]

with a transom height to suit a long shaft, it seems that you should use one, unless you want to raise it up somehow.

[ahoj]

One wanders why boat builders do not stick to standard sizes for transoms there are mostly short shaft and long shaft and yet the motors and transom are different No wander the outboards do not fit.. One has to be very clever now to match the outboard with tramsom... 1-2or3 inches and trouble starts

My sixpence worth Ahoj

My mariner short shaft is from top hook -up to cavitation plate 47 cm or 18.5 inches
the yamaha long shaft is 57 cm or 22.5 inches--- Now you see how chaotic this is
To set your transom to the mariner the transom should be 44 cm 17.5 inches high ---and the yamaha long shaft should have a transom 54 cm or 21.5 inches. I quarantee your transoms are different lenghts-depths The better matching Transom to your outboard the better the performance

Cheers

[ahoj]

Sportfish.. it appears that the so called 20 inch shaft is NOT the correct one your cavitation plate is 2.5 inches above where it should be and the 25 inch will be too deep and will cause you spray and go slower. That means your transom either needs cutting down or build up
Your cavitation plate should be 1 inch below your lowest part of your boat floor

Ahoj

[Noelm]

ahoj, not always the case, it takes some testing as sometimes (usually) the best position is above the bottom of the boat and quite often quite a bit, a lot of things come into play here including the prop type and size.

[ahoj]

But its mighty close i use outboard bracket for my cat only--- as the hight of open water changes with the speed although i do have a skid plate at certain depth... its a bit complicated with cat hull its-- a lot easier with Mono
Ahoj
Noelm
with your assessment to above bottom line it depends how far your motor is from the transom the closer it is the lower you have to go-- load distribution is also a factor but i agree a foreplay is needed to have a perfect boogie....
A

[sportfish550]

Just one thing that i have forgotten to mention is that when i measured the transom height i measured it from the top of the pod to a stick which was inline from the keel going back to the engine (because the pod isnt inline with the transom)

[sportfish550]

sorry guys, but the stick i used to measure the transom wasnt straight & it gave me an incorrect reading. I redone it with a flat straight piece of aluminium(it is 20inches from the transom to the cav plate) does that sound right ?????????

[dnej]

It is no trouble to raise the mounting height,take it to a good aluminium boat builder, and get it done.
This will then raise your motor further out of the water. This is a great benefit when reversing,or when fishing in a swell,or even when stopping.I went from 20 inch to 25, and I would never go back.What type of motor you thinking about?
David

[sportfish550]

im not sure what motor im going to get but at the moment what ever i look at have 25inch shafts (my luck)!!!!!!!!!!.

[dnej]

Think positive.25 inch transom mount motors are great, for the reason I put in my post.
However ,if you want a 25 inch in a 70 hp Yamaha,they dont make them,yet in the 90 they do.
David

[dnej]

This may help you

[Sportfish_5]

Your engine will have a model code that will tell you what length leg it has. If it is a 20inch leg then you have no other choice but to fit that size unless you want to modify the pod.

Your Sportfish could have a 20 inch transom built but the majority would be 25 inch to keep the power head up away from the water but it depends what the spec was when it was built.


Cheers

Greg

[spearfish_1]

the cavatation plate should be level with the bottom of the boat