VeeDrive - loss of hp?

There are a lot of misconceptions around about v-drives. The short answers is there is no more loss of power than a conventional transmittion of the same gear ratio.

Most gearboxes reduce the input / crankshaft RPM, via internal gearing, resulting in a lower output / propshaft RPM. There are some minor losses in power between input and output due in part to this gear train. Most modern V-Drives are variants of their equivalent parallel output and down-angle brothers, and share basic case design and much of the same gear train components too....the only real difference is that in a V-Drive configuration the input and output shafts are on the same face of the gearbox casing....the power losses for each configuration are all but identical.
There is a slight weight penalty to pay for with the V-Drive layout due to two additional shaft flanges, Cardan shaft, additional (usually heavier) mounts and in most cases an engine bell housing.
Against that, common benefits are...
The ability to move a large mass further aft (useful if applied to fast planing craft requiring an LCB biased aft)
The dramatically shortened propulsive machinery installation space required, as the engines are aft of the gearbox instead of fwd of.
In certain cases, the option of ridgidly connecting the gearbox to the propshaft, without the need of a flexible coupling to take out the inherrent shaft bending tendency of a flexibly mounted engine and close-coupled gearbox.
In certain cases, the benefit of designing a drive train that can transmit thrust directly to the boats structure, rather than through a flexibly mounted engine and close-coupled gearbox.

Let me know if you need assistance with the exhaust system for your v-drive application.

+ As said, your speed may be higher, because you can fit bigger and slower-turning propellers (with bigger reduction ratio gearbox) with the same propeller tip clearance.
+ Also your shaft angle may be smaller which helps too.


- You will have a cardan shaft which needs replacement at certain intervals (check with supplier).
- If one of the cardanic couplings would ever fail, the spiralling cardan shaft would likely carve a large hole in your engine room bottom.
- You will need to build a protective cover over the cardan shaft.
- As mentioned, weight and cost will be higher.
- The gearbox has to take up the thrust, and this source of noise will be located closer to the accomodation (assuming to be located fwd of the engineroom bulkhead). It's not possible to work with a separate thrustbearing which is a more quiet solution.

Bruno