Prop Shaft Size?

[kylerichmond]

HI
I currently have a UFO34 sailing boat fitted with BMC 1.5 (35bhp) and a 7/8 ins propshaft.
However we are wanting to change this for a larger engine such as a Peugeot XUD 1.9 (59bhp).
Would this shaft be ok? or would i have to change it

 

[sailorman]

you can never absorb 56hp in a UFO34
35 hp is more than enough so if you de-rate the other engine to 35hp the gear would do though i would have a 1.25" shaft with 35hp

 

[Koeketiene]

Our engine (Vetus) is based on the Peugeot XUD 1.9.
And we have a 30mm prop shaft.

Are you sure you need that kind of power in your UFO? /forums/images/graemlins/confused.gif

 

[pvb]

[ QUOTE ]
....though i would have a 1.25" shaft with 35hp

[/ QUOTE ]My 43hp Volvo has a 25mm shaft. Seems OK.

 

[nedmin]

My last boat had 2X62hp engines propshaft was 40mm.

 

[Tranona]

A 7/8 inch shaft is too small even for 35hp. The minimum would be 1 inch or 25mm, but more usually with that engine 1 1/4 inch or 30mm. You do not need 56hp as there is no way you could use the power. 30hp with a reduction gear is more than enough with a 1 inch shaft

 

[Strathglass]

The shaft size is related to both engine size, gearbox ratio and prop size.

With a very large prop and a high reduction ratio in the gearbox then a larger diameter of shaft is required to handle the torque.
Conversely with a smaller prop which will require to rev faster a smaller shaft can be used.
There are programmes available on line to enable you to calculate which series of variables are required.
If you know the BHP of the new engine and the reduction ratio of the new gearbox then you know the shaft RPM and can calculate the prop size and diameter required.

My feeling is that your shaft is a bit slender.

I use an 1 1/8" shaft on a 40 HP XLD with a 2:1 reduction gearbox.

I am sure you could Google engine /propeller ratios or a formite could post you a link.

Iain

 

[TigaWave]

There are several factors involved to ensure a correctly spec'd shaft size.

To provide accurate information we would require.
Engine make
HP
Rpm
Reduction ratio
Shaft length, number/length of bearings supporting shaft.
From this we calculate delivered torque and quote torsional yield.

 

[Seanick]

If you are worried that you are on the limits, Lake Engineering offer a stainless alloy called 'Lakemet' which can absorb (i think) 30% more power, thus saving changing your tube etc.


I ran a pair of Perkins 4107's through 10 foot shafts, unsopported for 5 feet. Contrary to the prophets of doom, they ran true, never buckled, and the props never fell off in 15 years of flambouyant driving. So that 45HP through an 1 1/8 shaft via a 2;1 box.

However my professional advice would be that with your current shaft you are on the limits, and I wonder what your max diameter prop is that you can throw to load the engine enough to not give you trouble later on. If you can spin the right prop, then it won't help your sailing performance!
I wouldguess at a 18" x 12 or there abouts!

 

[Heckler]

Beneteau fitted a 25 mm (1") shaft to my old 351 with a 30 hp VP2030, my 381 has a 30mm shaft with a 50hp engine so 7/8ths a bit thin
Stu