PRM 150 1:2.09 and bullflex 8 weight

[Tresfjord26]

Hello

I have a beta 43hp 2800rpm engine and a prm 150 1:2.09 gearbox on my tresfjord 26 boat

the propeller shaft is 35mm and 1.8 meters long. Weights aprox 13,59kg
propeller is a 17x14 3-blade that weights 7.7kg?

Im now fitting a vetus flexible coupling Bullflex type 8, it weights 11.9kg
Smaller bullflex 4 would otherwise be fine for my gearbox but they dont make it for 35mm shaft

The thing that troubles me is the shaft weight that the gearbox has to rapidly accelerate when engaging a gear. Will this bullflex absorbe the impact of rapid acceleration eaven tough it is quite massive and add extra weight to my shaft configuration
or eaven if i have to do a emergency forward to backwards gear change
Im worried about gearbox clutch plates wearing out faster than normal beacose of this.


shaft, coupling and propeller weight combined is 32.2kg

 

[Divemaster1]

Welcome to the asylum !! Tresfjord 26 brings back many memories (only seen one in the UK and that was in Kirkwall)...

To help others;

Cannot help you with your technical query, but have experience with Tresfjord 26 with a Volvo petrol, which we swapped out for a 4 cylinder 54 hp Ford, A Tresfjord 26 with rigging (not many were made) and very over powered with a 80 hp Ford, followed by a Tresfjord 28 with a 49hp Perkins ... happy days !!

 

[Arcady]

I have a Bullflex 8 on a 35mm shaft coupled to a 42 hp Vetus diesel with mechanical ‘box. It’s fine. Most of the weight of the Bullflex is in the clamp coupling and is isolated from the engine by the rubber - which is good st absorbing torsional stress. It’s proven to be a quiet and smooth installation for us.