bow thruster affect on sailing performance?

[contessaman]

10m yacht. how much would fitting a bow thruster adversely affect sailing performance?

The advantages of having one for short/single handed sailing are obvious. from first principles I can see 3 dissadvantages performance wise:

1) increased form drag due to laminar flow being disturbed due to hole through hull.

2)slight loss of lateral area and hence resistance to leeway due the hole through the hull

3)loss of performance due to added weight of bow thruster plus its own battery, also undesireable affect of weight being distributed in the bow of the boat.

so thats the science. but what does all that actually equate to in a 10m yacht? I put the question to you my yachtie cyber chums as im sure a great many of you have fitted them to such a boat and can report to me first hand on the affect or otherwise on sailng performance.

over to you...

 

[MoodySabre]

A bit of reading:

http://www.ybw.com/forums/showthread.php?t=230227

http://www.cruisersforum.com/forums/f47/bow-thruster-48416.html

http://www.max-power.com/Product-Selection/Retractable-Thrusters.html

 

[SHUG]

You will lose about half a knot and gain a lot of hassle

 

[Ex-SolentBoy]

You will lose about half a knot and gain a lot of hassle

Surely this will depend a lot on the shape of the fairing around the thruster tunnel.
I have a sneaking suspicion that if properly faired the drag will be miniscule - certainly not enough to cause a 5% reduction in speed.

Any real hydro-dynamic experts out there?

Sidepower say:-
1. The best solution which normally reduces the drag most is to
make a recess in the hull at the back of the tunnel. Thereby the
back face is gone and about all the drag (Fig. 2). The depth and
shape of this recess will depend on the boat. Basically you
should
not see the back face of the tunnel when standing directly in front
of the tunnel at the angle of the boats centreline. The angle up or
down backwards of the insert in the hull, depends on the
hullshape, but normally it is angled slightly down because of the
water flow on this area of the hull.
2. The drag will also be reduced a lot, especially in fast power
boats,
by making a deflector / spoiler in front of the tunnel. This will push
the water flow out from the hull so that most of it passes by the
back face of the tunnel (Fig. 3). The shape and size of this
deflector will depend on the hull shape. Basically you should not
see the back face of the tunnel when standing directly in front of
the tunnel at the angle of the boats centreline. The easiest way of
making this is to let a part of the tunnel stick out in the lower
forward area of the hole, and use this as a support to mould a
soft
curve/spoiler shape.

 

[Poignard]

Your username suggests you're thinking of fitting this to a Contessa. In which case, why not contact Jeremy Rogers for advice?

http://www.jeremyrogers.co.uk/

 

[Tom Price]

The only reason for fitting one is to reduce hassle surely?
That's the whole singlehanded parking circus.

Sailed a Conti 32 for years and never even thought of it!

 

[BoyBlue49]

Bow Thruster

Unlikely you will be able to mount it far enough below the water line to eliminate cavitation on a 10 meter yacht.

The top of the tunnel needs to be at least 6" below the water line. Can you achieve this ?

Fairing does help with drag. Not an issue IMHO.

Negligible loss of leeway.

In a 10 meter yacht, not at the top of my wish list. 15 meter + yes.

Expensive toy of little use.

 

[SailBobSquarePants]

In a 10 meter yacht, not at the top of my wish list. 15 meter + yes.

Expensive toy of little use.

You've obviously never tried to put a 32' full keeled boat into a marina berth on the Hamble in a cross current...

And at my (tiny) marina I know lots of long fin keelers that have problems with the tight spaces and crosswinds...including Contessas.

So blankets statements really not that helpful.

If you (the OP) single hands a lot, and don't race, and have a few thou...go ahead. I would recommend the wireless remote if you have a tiller as well, makes single hand docking much easier. We love ours in a Nich 32...

 

[Blueboatman]

And very antisocial to your neighbours upon an early morning departure-although probably less so than an unplanned collision!

Invest in a couple of 'hands on' lessons under power firstly perhaps?

Personally I would begrudge the loss of storage space.

 

[contessaman]

Your username suggests you're thinking of fitting this to a Contessa. In which case, why not contact Jeremy Rogers for advice?

http://www.jeremyrogers.co.uk/

sorry my user name is misleading. I did have a contessa. but it was a 34ood not a 32. that boat did not need a bowthruster as it had a really deep keel and a huge spade rudder. save the folding prop issues it was a doddle under power. alas it was not a good family boat so I sold it Im now looking at family orientated cruisers the same sort of size. Got my eye on moody eclipses. of the ones I have looked at about 50% have bow thrusters. I know the fin keel eclipse actually sails quite well (not a patch on my former ride). Im clearly giving up a lot of performance anyway in favour of a boat that me wife and newborn baby will actually get some use out of. Eclipse has lot more windage than my old tessa and a lot less below the waterline. so the conundrum is a bilge keel eclipse with a bow thruster (easy to handle, dry out) or an un molested fin keel one which will at least satisfy my enjoyment of a sailing boat that can actually sail, albeit not going to win me any silver.

you are dead right about jeremy though. he's a legend. my dad has a contessa too. you can ring jeremy up and he remembers every single boat that he has built. any tech questions or anything else he's so happy to help. he even still makes spares.

 

[mattnj]

Without sounding rude, perhaps get some pro help in manovering first, dont reckon you need one.

 

[Tranona]

sorry my user name is misleading. I did have a contessa. but it was a 34ood not a 32. that boat did not need a bowthruster as it had a really deep keel and a huge spade rudder. save the folding prop issues it was a doddle under power. alas it was not a good family boat so I sold it Im now looking at family orientated cruisers the same sort of size. Got my eye on moody eclipses. of the ones I have looked at about 50% have bow thrusters. I know the fin keel eclipse actually sails quite well (not a patch on my former ride). Im clearly giving up a lot of performance anyway in favour of a boat that me wife and newborn baby will actually get some use out of. Eclipse has lot more windage than my old tessa and a lot less below the waterline. so the conundrum is a bilge keel eclipse with a bow thruster (easy to handle, dry out) or an un molested fin keel one which will at least satisfy my enjoyment of a sailing boat that can actually sail, albeit not going to win me any silver.

Think your explanation says it all. If 50% of owners have gone to the expense of fitting one then they either find them of value or have been on the receiving end of a very persuasive salesman! I doubt it would make any noticeable difference to sailing performance. The downsides are the space it atkes up and the power it consumes.

To find out if it is value for you, then ask the owners or better still try with and without.

 

[dunedin]

Sounds like horses for courses, as ever

A modern fast fin keeled 10m boat probably doesn't need a bow thruster at all - which is good as the depth at the front will be too shallow to fir, and the tunnel will inevitably slow things down in lighter winds

A heavy long keeler probably will benefit most due to wayward reverse characteristics - and fortunately should have enough forefoot depth to fit and is pretty likely already slow in light winds anyway, and will be marginal difference when get nearer hull speed in a strong blow

A Moody Eclipse is somewhere in between - great cruisers but not particularly fast light wind sailer, and bilge keel more so. Also high windage and wheelhouse attractive to many more mature (!) yachtsmen, hence the very high percentage fitted for such a small boat

 

[contessaman]

been manoevering boats for over 50 years, always with warps, never thought I would need a bowthruster, then I bought one (under extreem duress! you old the boat is too big, lots of windage kind of arguments - get one or loose a crew worked) love it to bits. Thinking of adding a remote capability.

its funny to see my internal differing opinions being thrashed out on this thread by others. I was such a purist, from the type of boat I owned, the equipment it had (tuff luff + lots of headsails) and they way I operated it.

On the other hand there have been so many days where I have sat in the marina because although I had a thoroughbred boat the particular family crew I had meant I had to make a tough call as any good skipper should make and accept that the crew were not up to sailing in the prevailing conditions. Meanwhile the big white bath tub next to me with bow thrusters, roller furling and electric windlass etc etc crewed by a couple old enough to be my grandparents was off for a sail.

Its not that there was not a way of taking my boat out - springing off or putting a slip on an upwind pontoon. we could do the sails too, using the tiller pilot and both of us. Its just that all these things made it unpleasant for my other half. And based on the fact that any sailing is better than no sailing im a bit of a convert.

the one area I will not conceed to though is that I feel a yachts ability to sail to windward or be sailed to windward by her crew is paramount to her seaworthiness. I was hence wondering if a fitted bow thruster would severely hamper this.

 

[SailBobSquarePants]

Its just that all these things made it unpleasant for my other half.

Which is EXACTLY why my Nich 32 has one...one time in the Hamble she was reduced to tears after a particularly bad docking attempt. £3500 is a cheap price for domestic harmony...

And Marsupial, get the remote...you will wonder how you lived without it...

 

[CAPTAIN FANTASTIC]

I am aware of some yachts who have installed external, removable, bow thrusters.

 

[Boathook]

Without sounding rude, perhaps get some pro help in manovering first, dont reckon you need one.

I fitted a Vetus unit quite a few years ago. Try not to use it but it was / is one of my better investments, especially as my boat does not go astern very well.

 

[BAtoo]

Learn to handle the boat properly and save your money then you wont have to worry about loss of performance, or worrying the neighbours etc, come on its only 10m long, and if its a Contessa its not a full long keel.

 

[Tom Price]

So this is a matter of seamanship. Perhaps we could learn from a recent post on the MoBo pages:

"Communicate with your crew, ideally in advance so everyone knows what you expect of them. SWMBO does all my ropes, I have offered to swap but she is happiest with a rope or fender in hand. I tell her what I am planning to do well in advance, ie when going home to Burseldon we discuss wind and tide conditions, which is stronger etc, while travelling up the Hamble, so when there have plan A and B ready to go.

+1 to getting lots of practice!!! I made a complete mess of berthing my current boat until we put aside some time to understand "what the boat did when..." and also to work out and repeat a "usual" routine.

You're absolutely right about getting a line on somewhere as this gives you lots more options. My aim now is to get confident/good enough to do it single-handed. Lots of lassooing practise from the mid cleat this July!!!"

I suggest that approach, even to the extent of booking an instructor for a short tuition session, rather than consider a bow thruster.

 

[Elessar]

Without sounding rude, perhaps get some pro help in manovering first, dont reckon you need one.

Not need maybe, but they enable you to get into berths/situations that would be impossible without one, no matter how well trained. A very useful tool in the modern crowded marina environment.