vic008
Well-Known Member
31ft yacht: Installing a 20hp engine on rubber mounts.Surely a thrust bearing will be required, although none of my research says so. How else would the thrust be transmitted to the hull?
thrust bearing reqd?
- Thread starter vic008
- Start date
Talulah
Well-Known Member
Through those rubber mounts.
fisherman
Well-Known Member
If you want a lovely quiet vibe free installation use an Aquadrive. There will then be a thrust bearing just ahead of the stern tube, and the drive shaft between that and the engine, which will need a lot less alignment, can be up to 16 deg off, according to:
http://www.tnorrismarine.co.uk/flexible.php
http://www.tnorrismarine.co.uk/flexible.php
sailorman
Well-Known Member
30boat
N/A
I'm for the Aquadrive but the flexible mounts will be perfectly capable of taking the thrust.
Bilgediver
Well-Known Member
The bearings in a marine gearbox are designed to take the engine thrust. This is quite normal though some folk do install proprietary thrust bearings and
universal joints to allow the engine to move around on its mounts without wobbling the shaft.
It is important to ensure that the shaft is centralised in the stern tube and that the seal you use is tolerant of the fore and aft movement of the engine between running astern and ahead.
Ric
Well-Known Member
On a 31ft boat it is usual for the thrust to be transmitted to the hull through the engine mounts.
However, if you fit an aquadrive you can mount the engine on much softer blocks and so have less vibration transmitted to the hull.
However, if you fit an aquadrive you can mount the engine on much softer blocks and so have less vibration transmitted to the hull.
Neil_Y
Well-Known Member
The simple set up is as mentioned thrust is taken in the gearbox on a thrust bearing internaly and transmitted through the rubber mounts.
The alternatives are a Hydradrive or an Aquadrive or simpler and cheaper (not thrust but CV) the Marine joint which allows for misalignment as the engine moves on its mounts whilst allowing the shaft to run true without side thrusts.
http://www.thermoboat.com/ptmarine.htm
We can get them but we've stopped selling them as we're too busy with bearings!
The alternatives are a Hydradrive or an Aquadrive or simpler and cheaper (not thrust but CV) the Marine joint which allows for misalignment as the engine moves on its mounts whilst allowing the shaft to run true without side thrusts.
http://www.thermoboat.com/ptmarine.htm
We can get them but we've stopped selling them as we're too busy with bearings!
charles_reed
Well-Known Member
Most small boats have a "soft" drive with the load transmitted through the shaft clamp to the engine mounts.
Yanmar bearings are extremely soft, despite that it seems to have worked quite well on my boat for 22 years and 2 engines.
One word of warning, in ahead the shaft is pushed into the shaft clamp, in reverse, with an Autoprop which is as efficient in reverse as forward gear, the shaft can be pulled from the clamp, if one is too enthusiastic in reverse gear.
Unfortunately, in most boats of 31', there is insufficient room to fit any of the proprietary thrust bearings.
Yanmar bearings are extremely soft, despite that it seems to have worked quite well on my boat for 22 years and 2 engines.
One word of warning, in ahead the shaft is pushed into the shaft clamp, in reverse, with an Autoprop which is as efficient in reverse as forward gear, the shaft can be pulled from the clamp, if one is too enthusiastic in reverse gear.
Unfortunately, in most boats of 31', there is insufficient room to fit any of the proprietary thrust bearings.
