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Old 15-08-2012, 23:33   #76
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Re: Hmmmm - Bowthrusters ??

You're just not catching on. If you were doing nine knots with a 40 percent main that tells me one thing-there was plenty of wind. No one here is saying you will lose half a knot on all points in all conditions with every boat and every install. That's not how the real world works. If you had carefully recorded your boats speed on all points in varying wind strengths before the thruster and then done the same after, you would see differences. Particularly to weather and particularly in light airs. The very fact that you would explain it away in this fashion tells me you don't understand. Just because your boat will still hit hull speed at a given wind strength doesn't mean much.
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Old 16-08-2012, 02:14   #77
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Re: Hmmmm - Bowthrusters ??

I think i am catching on real fast ..

You're one of those guys with opinions based on their own self generated assumptions

1) There wasnt "plenty of wind" as you put it - we had some gusts of up to 20 knots but generally wind was 15-18 knts.

2) 40% main up doesnt always reflect lots of wind in any case - i prefer to sail flat and have a killer combo cutter rig which works like a treat . Keeping the in-boom furling mainsail trimmed is mainly because i like to sail fairly flat

3) Hull speed is higher than 9.1 knots - we hit 9.6 knts during one of the gusts

If i did what you suggested , i wouldnt be out there sailing in Thailand right now

Thanks for the free advice though ....

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Old 16-08-2012, 02:47   #78
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Re: Hmmmm - Bowthrusters ??

My view is that if the wind or current is strong then an outboard on a dinghy is far more useful.
Either to take a line ashore or pontoon, or to tie on to a buoy and then receive a line from the 'mother ship'. For smaller boats a kayak is just as useful, except as a tug.
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Old 16-08-2012, 03:07   #79
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Re: Hmmmm - Bowthrusters ??

Nothing wrong with having a bowthruster if that’s what you want, as for the loss in performance ?? just going on the increasing amount of new builds with bowthrusters and older vessels been retrofitted with them, i don't think the owners really care.....
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Old 16-08-2012, 03:51   #80
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Re: Hmmmm - Bowthrusters ??

Lets get a few things straight. BTs are great during docking (I've many years without one so I do know how to dock without one). During docking we don't give a damn about loss of speed.

If we are going blue water cruising - we may (repeat may) care about speed, but in general we are cruising and if it takes us an extra half or whole day to cross the atlantic - well so be it. Assuming a BT really does depreciate performance by that much.

If the wind gets up around 20 knots - I'll be running at hull speed anyway so who really gives a damn? I am not a racer. My boat begins to move at just under 5 knots by 20 knots I'm hull speed.
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Old 16-08-2012, 03:52   #81
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Re: Hmmmm - Bowthrusters ??

Someone further up this thread asked if anyone had ever gotten anything in their BT. This summer I swallowed a plastic bag during docking. stopped the B T dead. Good thing I'm a diver and carry scuba gear on board. 10 minutes under water and it was ll cleaned out and the BT working like a charm again.
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Old 16-08-2012, 06:02   #82
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Re: Hmmmm - Bowthrusters ??

So in conclusion...

The "experts", stated a bow thruster is bad for hydrodynamitcs, but would not give an opinion because there are too many variables. We all know anything on the hull will effect hydrodynamics (Even Barnicles), but how much and what is is reasonable?

Only one person stuck his neck out and claimed a 1/2 knot loss of boat speed due to the bow thruster's hole, but that makes a lot of assumptions, based on "the experts" variables of crew, fuel and other weight, not to mention if the thruster is faired or not.

A couple of people made mention of not using thruster when cruising because they wanted speed. Here is news for you.... Most people who convert their boats from a weekend warrior to a fulltime cruising boat raise their waterlines from 1 to 2 inches before leaving. Good luck with speed!

Cavitation can be an issue. This normally mitigated in Recreational boats by having chain in the chain locker and a anchor on your bow.

Oh and lets not forget the people that have decided that bow thrusters are "evil" because you loose your sailing skills... I won't even respond to that STUPID theory....

Those of you talking about race boats and bow thrusters.... Are you nuts... Why even go there? People go to the point of wet sanding their hulls for a 0.10 more speed, make crewman empty their sea bags before stepping on board and spend hundreds of dollars more on things like ultra light blocks to save weight. A bow thruster... Please!

So finally, the people that said they owned bow thrusters, stated they liked them and some said they would not own another vessel over a certain length without one.

In fact, I don't recall one person who actually owned a bow thruster say they hated it or removed it because it made their boat to slow.
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Old 16-08-2012, 06:15   #83
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Re: Hmmmm - Bowthrusters ??

It is truly amazing to read how many boat owners claim their boats to consistently hit hull speeds. I guess this is mid latitude sailing? When it is flat, you motor; when it blows 40 knots, you go sailing.

A typical ocean passage maker may find it pretty hard to get consistently close to hull speed. Trade winds are not as strong as mid-lat winds, swell is higher and boats carry big amounts of water, fuel and extra equipment.

I run a quick analysis of a couple hundreds of ARC boats and compared the results with a similar analysis of Transpac resluts. It is public data and everybody can go and see for themselves. Things like 0.9-1.0 sqrt LWL are possible, 0.7-0.9 is the norm. Below 0.7 are the pigs, above 1.0 are the racing multis and some very sleek monos.

I think the speed loss may count nothing when the boat goes fast but when most of the voyage is done at say 0.8 (say 5 knots in an average 40'er) then half a knot is 10% speed loss that translates into a 10% longer passage.

Having grown up in the world that ALWAYS hurries I think very few cruisers would escape the temptation to go get that extra 0.5 knot! Of course, since the benefits from bragging about my bowthruster are bigger than the benefits of going that 0.5 kt faster, I went for the BT!!!

;-))))))
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Old 16-08-2012, 06:26   #84
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Re: Hmmmm - Bowthrusters ??

Quote:
Originally Posted by jeremiason View Post

A couple of people made mention of not using thruster when cruising because they wanted speed. Here is news for you.... Most people who convert their boats from a weekend warrior to a fulltime cruising boat raise their waterlines from 1 to 2 inches before leaving. Good luck with speed!
+1!

But a heavier boat PLUS some highly hypothetical speed loss from having a bowthruster PLUS ...., then how much total speed loss is this?

As we make our boats heavier and we keep on adding more toys like bow thrusters, we are making ourselves less and less sailors, more and more cargo ship crews.

With the congestion in the modern marinas, can we escape the BT?

I do not think there is any clear cut answer other than along the general line of 'if you need a BT (or if you badly WANT one) get one!

b.
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Old 16-08-2012, 06:57   #85
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Re: Hmmmm - Bowthrusters ??

Quote:
Originally Posted by barnakiel View Post
As we make our boats heavier and we keep on adding more toys like bow thrusters, we are making ourselves less and less sailors, more and more cargo ship crews.
I think you have a valid point about how much weight we carry, but in my opinion having bow thruster on my boat, doesn't turn it into a cargo ship.

The extra manuverablity a bow thruster adds, allows me to get into places that other boats of similar size can't. It allows me to get off windy docks, without the hastle of setting up spring lines and it allows better more control when I back my boat.

For me that is worth the extra 44 pounds of weight that my bow thruster adds!
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Old 16-08-2012, 07:54   #86
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Re: Hmmmm - Bowthrusters ??

I just read this thread from start to finish, including the stupid-ass remarks from some arm-chair experts.

I could not help but think that it is too bad that Henri Amel is dead. He could have contributed actual knowledge to this thread. I will attempt to pass on some of his knowledge: Did you know that 100% of all sailboats produced by Amel from the mid-80's through today have retractable bow thrusters? This is not an option. Amel tested tunnel types and found a slight loss of speed, a big loss in thrust because of the tunnel, and lots of other problems like creature growth, etc. He decided that there was not a solution available that suited him, so he designed and manufactured a retractable 10hp 24v electric bow thruster. This was used on all of his boats until the mid 2000's when Amel switched to a commercial retractable bow thruster that was satisfactory to them.

Dockhead summed up the features of a bow thruster in a few posts back, including the ability to move the boat sideways. You can also steer a boat from the front and back (BT & Rudder) simultaneously. The longer the boat, the more useful this is. BT's are wonderful while maneuvering in reverse...place the rudder amidships and steer with the BT.

No one really stated what we all know and that is all boats are different. Some very easy to maneuver with no skegs on the rudder, winged keel, etc. Others are much more difficult with skegs larger than the rudder and full keels. Some boats enjoy great prop-wash, others, none.

Personally I believe that most production sailboats of 50' or more need a bow thruster and some need it more than others; I also believe a sailboat under 40' does not need a bow thruster, but obviously there are benefits.

We have been circumnavigating for 7 years and have met lots of real cruisers. I do not think I have met anyone making passages who does not care about the gain or loss of 1/2 knot.

Bill
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Old 16-08-2012, 08:32   #87
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Re: Hmmmm - Bowthrusters ??

I love my bowthruster and I don't feel I lose any speed, it was installed professionally and faired in brow ahead of it by previous owner, but I can not prove there isn't a loss. My wife likes it even more. As were getting old and our ability to get off boat quickly has slowed us down this tool makes life easier and safer. Our marina is extremely tight, little room to turn, 3kn side current and lots of wind with neighbor 4 feet away. Long keel slow turning 40' Cape Dory needs all the help I can use. No cavitation and nothing has ever got in prop.
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Old 16-08-2012, 08:47   #88
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Re: Hmmmm - Bowthrusters ??

Quote:
Originally Posted by minaret View Post
Racing boats use extendable thruster tubes for this reason, I have installed many. They are extremely expensive. People don't install them for no reason. I said I had recorded about a half knot difference, not a knot.
That half-knot figure would be specific to that installation and that hull form. It would also be subject to accurate measurement, something which would require a great deal of effort (averaged two-way runs in well controlled conditions, sea state, revs, etc.). Without accurate measurement, it would be more of a guess.

I have no idea how much drag is caused by my BT installation because all Moody 54's were built with them. There is no boat like mine without a BT to compare to.

As far as I understand, a lot depends on the right fairing of the tube opening. Without any fairing, quite a lot of turbulence is created, and I can imagine even more than a half-knot of lost speed in some cases.

I'm sure it also depends greatly on the relationship between the tube size and the total wetted surface of the boat. So logically small boats would suffer a lot more, maybe tremendously much more, than larger boats, from turbulence around a bow thruster tube.

So I really don't think any easy rule of thumb can be applied.
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Old 16-08-2012, 09:01   #89
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Re: Hmmmm - Bowthrusters ??

Quote:
Originally Posted by barnakiel View Post
It is truly amazing to read how many boat owners claim their boats to consistently hit hull speeds. I guess this is mid latitude sailing? When it is flat, you motor; when it blows 40 knots, you go sailing.

A typical ocean passage maker may find it pretty hard to get consistently close to hull speed. Trade winds are not as strong as mid-lat winds, swell is higher and boats carry big amounts of water, fuel and extra equipment.

I run a quick analysis of a couple hundreds of ARC boats and compared the results with a similar analysis of Transpac resluts. It is public data and everybody can go and see for themselves. Things like 0.9-1.0 sqrt LWL are possible, 0.7-0.9 is the norm. Below 0.7 are the pigs, above 1.0 are the racing multis and some very sleek monos.

I think the speed loss may count nothing when the boat goes fast but when most of the voyage is done at say 0.8 (say 5 knots in an average 40'er) then half a knot is 10% speed loss that translates into a 10% longer passage.

Having grown up in the world that ALWAYS hurries I think very few cruisers would escape the temptation to go get that extra 0.5 knot! Of course, since the benefits from bragging about my bowthruster are bigger than the benefits of going that 0.5 kt faster, I went for the BT!!!

;-))))))
b.
I have argued against this 0.5 knot penalty as a flat rule of thumb above.

I agree with others that speed is extremely important, and if I thought my BT was costing me 0.5 knots, I would seriously consider changing it for a retractable one (I would bet the designer would have specified a retractable on in this case anyway).

I doubt that it costs me 0.5 knots.

Hull speed on my boat is either 9.1 knots or 9.6 knots, depending on which calculator you use. I cannot sail my boat at hull speed for sustained periods of time unless it is really blowing hard.

But my average long passage speeds are typically well over 8 knots. My English Channel crossings (80 to 100 miles in the places I do it) are typically on a pace for a 200 mile day, so over 8.3 knots. We do have good wind in the English Channel, usually, but still I think this is pretty good performance for a heavily loaded cruising boat, considering I have 12 year old sails and that I am not an ace sail trimmer. It doesn't seem to me that my bow thruster is holding me back much, and I have never given any thought to spending money changing to a retractable.
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Old 16-08-2012, 09:45   #90
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Re: Hmmmm - Bowthrusters ??

Quote:
Originally Posted by svBeBe View Post
I just read this thread from start to finish, including the stupid-ass remarks from some arm-chair experts.

I could not help but think that it is too bad that Henri Amel is dead. He could have contributed actual knowledge to this thread. I will attempt to pass on some of his knowledge: Did you know that 100% of all sailboats produced by Amel from the mid-80's through today have retractable bow thrusters? This is not an option. Amel tested tunnel types and found a slight loss of speed, a big loss in thrust because of the tunnel, and lots of other problems like creature growth, etc. He decided that there was not a solution available that suited him, so he designed and manufactured a retractable 10hp 24v electric bow thruster. This was used on all of his boats until the mid 2000's when Amel switched to a commercial retractable bow thruster that was satisfactory to them.

Dockhead summed up the features of a bow thruster in a few posts back, including the ability to move the boat sideways. You can also steer a boat from the front and back (BT & Rudder) simultaneously. The longer the boat, the more useful this is. BT's are wonderful while maneuvering in reverse...place the rudder amidships and steer with the BT.

No one really stated what we all know and that is all boats are different. Some very easy to maneuver with no skegs on the rudder, winged keel, etc. Others are much more difficult with skegs larger than the rudder and full keels. Some boats enjoy great prop-wash, others, none.

Personally I believe that most production sailboats of 50' or more need a bow thruster and some need it more than others; I also believe a sailboat under 40' does not need a bow thruster, but obviously there are benefits.

We have been circumnavigating for 7 years and have met lots of real cruisers. I do not think I have met anyone making passages who does not care about the gain or loss of 1/2 knot.

Bill
Your comments about prop wash really hit home for me. My last boat had a two bladed prop just in front of the rudder. I got pretty cocky handling that boat in tight quarters. Using prop wash and walk I could spin that boat 360 degrees almost in a boat length.

THEN, fast forward to my latest boat. Didn't think about that issue too much until, on my first cruise with the boat I got into a tight marina with 2-3 kt current pushing me down a dead end fairway lined with goldplaters and I couldn't get turned around. Starting thinking very hard to remember if I had mailed my last insurance check. Basically the prop is far enough from the rudder and angled down enough so there is almost no prop wash effect. Until you get some headway the boat is going straight, period. Also very little help from prop walk as the prop is fairly far forward.

So, for the first time in my boating career have been thinking about a bow thruster. Put one on the list and it will happen as soon as I finish: standing rigging, mast overhaul, new halyards, holding tanks, refer, hot water, new bilge pumps, wiring, AC repair, AP repair, new steering cables, and about forty more things on the list.

PS

Did finally get the boat turned around and out of the marina with no damage to the "yachts" around me. As the current drove me closer and closer to the dead end where sat an 80' sloop with an awlgrip job that looked slick as a mirror I came to a slightly wider spot in the fairway. I backed in until my stern was a foot or two from the boat on that side, put it in forward and hit max throttle. The bow finally came around a couple of feet from the sailboat on the other side of the fairway, my sprit actually passing over their midships lifelines where a deckhand was sitting varnishing the toe rail. Her eyes were pretty big by the time we finally turned.

Spent a few days there and every day was a new episode of bumper boats. Just on my pier I saw two pretty good fender benders in three days. When we left we timed it for slack tide.
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