Pneumatic bow thruster

B

Barleycorn

Well-Known Member
Joined
22 May 2013
Messages
158
Visit site
I have just got a 27' boat with a single engine, and I was thinking of an easy and cheap way of controlling her when mooring back at the pontoon. A bow thruster would be nice, but £2500 is hard to find at the moment.
I just got thinking, what about fitting a largish air tank and a 12 volt pump to pressurise it. Then fit a couple of 1/2" skin fittings either side of the hull at the forward end. Then pipe them up to the air tank, with solenoid operated valves. I would think that this would give you enough push laterally to get you into a tight spot, and would be fairly cheap to do. Any views?
 
Don’t think you will get enough momentum transfer with air, it will just cause a awful lot of bubbles.

Vetus however used to do a bow thruster based on using water from an electrical pump and controlled by two solenoid valves to give port and stb thrust but I cannot find any ref to it so it may have been a no-go solution. If that did not work, the air will not do any better.
 
Air has a very low density vs. water so you'd need to move a lot of it very quickly to get a decent amount of thrust from an air jet.

However, an open rotatable tube with a 90 degree bend at the bottom could generate some suction. Just inject air at the bottom and it would rise to be replaced by water entering the bottom. The air wouldn't be at much pressure.

Don't see it as viable for lots of reasons (cost, performance etc.) vs. current designs.
 
FFS a 27' boat and you want a bow thruster - get out there man and learn how to manoeuvre her on the engine. If you cannot handle a 27'er on a single engine you need more lessons and/or practice or to take up gardening or needle craft instead.
 
cliff said:
FFS a 27' boat and you want a bow thruster - get out there man and learn how to manoeuvre her on the engine. If you cannot handle a 27'er on a single engine you need more lessons and/or practice or to take up gardening or needle craft instead.
Click to expand...

Harsh, but true!
 
Out of interest
Does the boat move towards the bubbles side or away from them?
I suspect it moves towards them

& yes other posts are right - you obviously need to learn how to handle the boat a little better
 
Daydream believer said:
Out of interest
Does the boat move towards the bubbles side or away from them?
I suspect it moves towards them

& yes other posts are right - you obviously need to learn how to handle the boat a little better
Click to expand...

I would think it would be away from the bubbles. The reaction is against the hull nozzle as the compressed air expands. The reaction between the air and water just limits the velocity of the air and speed that it expands. If one had aerated water along one side of their yacht, then the boat would move into the aerated water as the HH of sea water acting on the hull side with no aeration exerted a greater force, due to density of course. There will of course be a point where nozzle size, thrust from air and loss of HH due to water would cause the yacht to move into the bubbles. In the OPS case I think the water support would always be there such that the only difference is the thrust from the air expansion. Happy to be corrected. It would also be much noiser than current bow thruster technology.
 
cliff said:
FFS a 27' boat and you want a bow thruster - get out there man and learn how to manoeuvre her on the engine. If you cannot handle a 27'er on a single engine you need more lessons and/or practice or to take up gardening or needle craft instead.
Click to expand...
pvb said:
Harsh, but true!
Click to expand...
PC never was, nor ever will be, my strong point. The OP is (IMHO) a liability not only to himself, vessel and crew but also to other vessels (and crews) and needs to realise his limitations and get more training and/or practice in order to bring his boat handling skills up to an acceptable level - sounds like the lad who was "rescued" by the RNLI 9 times in one month AFTER having had his previous boat impounded.
While I have no wish to see compulsory training (and testing/examination) for general leisure sailing how long will it be before some jobsworth or other jumps on this issue due to "accidents" as a result of people taking to the water without proper, or should I say adequate, training. There is no need to go on RYA courses at extortionate costs, however training is available in most sailing clubs either by crewing for other members or having other members "crew" for you plus most clubs have theory courses (to varying degrees of formality) run over the winter months. The training is out there if one is prepared to put in a bit of effort and remember - experience is a great teacher - just get the experience safely.
 
cliff said:
.... The OP is (IMHO) a liability not only to himself, vessel and crew but also to other vessels (and crews) and needs to realise his limitations and get more training and/or practice in order to bring his boat handling skills up to an acceptable level - sounds like the lad who was "rescued" by the RNLI 9 times in one month AFTER having had his previous boat impounded...
Click to expand...

Your humble opinion is way over the top and there is nothing in the OPs post to sugest that the OP is a liability to anyone. It sounds nothing like the example you give or anything else that dramatic. It's just a poster asking about bow thrusters.
 
cliff said:
PC never was, nor ever will be, my strong point. The OP is (IMHO) a liability not only to himself, vessel and crew but also to other vessels (and crews) and needs to realise his limitations and get more training and/or practice in order to bring his boat handling skills up to an acceptable level - sounds like the lad who was "rescued" by the RNLI 9 times in one month AFTER having had his previous boat impounded.
While I have no wish to see compulsory training (and testing/examination) for general leisure sailing how long will it be before some jobsworth or other jumps on this issue due to "accidents" as a result of people taking to the water without proper, or should I say adequate, training. There is no need to go on RYA courses at extortionate costs, however training is available in most sailing clubs either by crewing for other members or having other members "crew" for you plus most clubs have theory courses (to varying degrees of formality) run over the winter months. The training is out there if one is prepared to put in a bit of effort and remember - experience is a great teacher - just get the experience safely.
Click to expand...

That's way over the top and very offensive. I would rather like a bit of bow thrust on my 33 foot long keeler. She is pretty 'non directional' astern. That said I ( and I guess the OP) understand my and the yachts limitations and take them into consideration.
The OP will probably do the same and will not be a danger to anyone.
 
My boat is useless astern. Worked out a seamanlike solution. Don't go astern! Simple. I now motor her into her berth and using two long warps, fore and aft, turn her from the safety of the pontoon, all ready to motor her out next trip. No shouting, no drama, no engine. Shown how to do it by a local who reminded me this was the only option before the days of engines. My boat is a 24', long keeler but I have seen him do it with 30' plus boats. He says that us leisure sailors are obsessed with trying to 'drive' our boats like cars. He may have a point!
 
Sophie19 said:
My boat is useless astern. Worked out a seamanlike solution. Don't go astern! Simple. I now motor her into her berth and using two long warps, fore and aft, turn her from the safety of the pontoon, all ready to motor her out next trip. No shouting, no drama, no engine. Shown how to do it by a local who reminded me this was the only option before the days of engines. My boat is a 24', long keeler but I have seen him do it with 30' plus boats.
Click to expand...

Years ago, we were allocated a particular tricky berth over winter. Tricky to get in and impossible to get out going astern.
So, we used to do that too. Not easy swinging a 44' boat around.
 
If you want the OP's idea to work, how about a tank in the bow nearly full of water but with compressed air at the top - then allow it to be forced out of a pipe on the side you want the thrust by a solenoid controlled valve.

Probably more complex and certainly heavier than a conventional bow thruster.
 
Last edited:
I agree with Hammer Man.
How totally ridiculous to contemplate having a bowthruster on a 27ft. boat. Anyone who would think to use one, must be totally incompetent, and unsafe to the rest of us nautical supremos. I would go further and jnclude auxiliary engines, heads, GPS navigation, radar, electronic depth sounders, in fact any electrics at all. Why not include all and every aid to ease?
Totally ridiculous.
And good luck to you.
 
I had a think about the use of compressed air.


If you use a jet of air within a tube of water, the air entrains the water and pushes it along. With a lot of bubbles etc, but a small high speed jet of water (which might be all that a 27ftr needs to encourage the bow to move to S or P) should in theory have a very similar thrust to a larger slower column of water.

You only have to feel the power of compressed air if you crack open a dive cylinder valve under water: it shakes all over the place.


Sounds like a good 3rd year project and thesis for one of the marine engineering students who appear here from time to time.
 
Last edited:
cliff said:
FFS a 27' boat and you want a bow thruster - get out there man and learn how to manoeuvre her on the engine. If you cannot handle a 27'er on a single engine you need more lessons and/or practice or to take up gardening or needle craft instead.
Click to expand...

You must come up to Scotland and try reversing my boat some time. I shall watch with considerable interest.
 
You must log in or register to reply here.

Other threads that may be of interest

lustyd
Fuel Gauge Calibration
2 3
Replies
45
Views
529
paulbrown22
P

Share this page

Top