It is normal practise to limit the number of holes passing through the hull of a seagoing vessel. However, Mersey class lifeboats have at least two more than the majority of craft. The red hatch cover in this photo shows our port-side 'freeing trunk' which is in the aftermost compartment of the boat called the 'tiller flat'. Even while at sea it is perfectly safe to remove this hatch cover as the trunk below extends above the waterline of the boat and so very little water comes in. The idea is that should a rope get wrapped around the propeller or propeller shaft and not be cut free by the shaft rope-cutter then it is possible to open the hatch and use a large knife (also stored in the tiller flat) to cut the rope free. In practice we have never had to do this, but we do deal with a great number of boats which have got ropes, nets or plastic bags wrapped around props and rudders. Perhaps if all vessels had a freeing trunk or other such precaution we might have fewer shouts to attend?
On the Inland Waterways all modern Narrowboats have one of these, except its described as a Weed Hatch. One detail they have is a 'Cavitation Plate' at the bottom of the trunk (usually attached to the hatch at the top so they are removed together). This fills the 'hole in the bottom' and keeps the water flow smooth - otherwise you get quite a racket as the wash from the prop churns around in the trunk.
ReplyDeleteIts very much needed - in some urban areas you can be 'down the weed hatch' many times a day.
You do have to watch yourself when using them though - I have a permanent scar on one arm from failing to notice some Barbed Wire that was mixed up with string and electrical cable. And for $deities sake switch off the engine (and put the ignition key in your pocket) before putting parts of your body near the prop.
Finally its also not unknown for people to forget to replace the hatch - the result can be a sunken boat as the water churned up by the prop is thrown clear of the top of the trunk and into the boats bilges. Once the stern sinks low enough that the top of the trunk is at the same level as the water a sinking is almost inevitable.
You may be amused by the following song which shows just why we have Weed Hatches on our Narrowboats:
(For the Perplexed 'Blades' is the more traditional canal boaters name for a Prop.)
Polly Round the Blades
(To the tune of "She'll be coming 'round the mountain")
If you like a spot of boating now and then
Take a tip and don't go on the BCN
It'll be days I can assure you
Before they come looking for you
And they don't take prisoners 'round at Windmill End
Chorus:
We've got miles and miles of poly 'round the blades
We've got miles and miles of poly 'round the blades
We've got miles and miles of poly
A tatty yellow brolly
And a supermarket trolly
'Round the blades
There are bags and bins put out by council men
But the Brummies they prefer the BCN
All their rubbish they have chucked in
This great big linear dustbin
It could do with being emptied now and then
Chorus
We've an eight mil porno movie 'round the blades
And we'd better watch it quick before it fades
Round to Tixhall we will fly
In the wide 'ole there we'll tie
We'll be safe there from constabulary raids
Chorus
We've a battered old Lambretta 'round the blades
We've a battered old Lambretta 'round the blades
We've a battered old Lambretta
A Marks and Spencers sweater
And a six foot long French ......
'Round the blades
Chorus
We've a forty eight D cup around the blades
We've a forty eight D cup around the blades
We've a forty eight D cup
A dead Alsation pup
And a horseshoe JUST FOR LUCK
'Round the blades
Chorus
What've we got?
Chorus
-- Ends --
Rick
Oh, and in my travels I have come across this. Its a bit pricey but it might save someone the need to call for assistance (I have no connection with the manufacturer by the way).
ReplyDeletehttp://www.bargee-bill.co.uk/propcleaner.htm
I do wonder whether it would be worth the RNLI trialling this bit of kit?
There are also 'Shaft Knives' available, rotating cutters that fit to the prop shaft and, hopefully, slice though stuff to cut it +before_ it gets tangled round the prop.
Rick
I can vouch for the need for a weed hatch on narrow boats. The photo at this link is of Steam Barge President with a load of cable insulation wrapped round the blades
ReplyDelete