Bow Thruster Oceanis 393

[bonny]

I'm thinking of fitting a bow thruster to my Beneteau Oceanis 393 but I suspect there are a few problems. I would be interested to know if anyone has one fitted, what make & model is fitted, performance etc.

Unlike most boats, the 393 has a walk through forward cabin to a forwards head. The problem is that the floor goes right forward, so no bunk to hide thruster in.
The only place I can see possible is behind the loo, under the forward holding tank. This does have the advantage that it's quite far forward so should give plenty of turning force, but unfortunately the draught this far forward is quite shallow. I've been told that a side-power 40 will fit but this seems a bit underpowered for a 12m (40ft) boat. Obviously I would like to fit a 60Kg model but I'm not sure if one will fit.

Other info:- I've had the boat for 5 years, which has a 3 blade volvo folding prop. Forward braking force is non-existant and she has tons of propwalk to port astern. I'm well used to handling her - even in tight quarters but a thruster - even an underpowered one will make things easier.

Any help or experience would be most appreciated.

 

[Silent Lady]

Bow Thrusters

We have a 323 and I was concerned about the depth of the tunnel .. The guy who fitted it glassed it in the bottom of the boat . You cannot get your hand under the tunnel as it is now part of the keel . I was worried about the minimum width etc but there is plenty of room . We have a forward bunk and room in front of the water tank but the thruster is still fitted at about 30 degrees to get it in . Well worth the hassel even on out twin rudder Beneteau . Makes playing around in tight spaces a bit more fun . Also fitted a seperate battery as you will find the cable runs are rather long to the engine start battery . Ours worked out at just over 10m so 140mm2 was required for the SE60 Sidepower . It turns the boat round with ease . Used a Sterling Battery to Battery Charger to recharge an AGM Battery and took the feed from the Engine Start battery .. Charger works when on mains or when engine is running . If you don't use the correct cable you get large voltage drops and less performance . So its not so much about the unit but how you supply the large amount of power it will consume . Local guy fitted the tube and SE60 and I did the wiring etc .. Brilliant .. Well worth it .. Even on a 323 ..

 

[SailBobSquarePants]

Worth it

I have a Side Power 40 fitted on my 32' Nicholson, which has tamed my full keel, even in marinas. Now, the 40 provides PLENTY of power to move my 7 ton full keeled vessel. Your boat is longer, but in terms of underwater resistance, and weight, I am probably pretty close to you. Your boat has more freeboard, so the wind effect will be larger however.

 

[Networks]

I am going through the same excersise on my 373. It has space forward of the under bunk water tank, but I have been told this space does not provide enough depth below the water line. Apparently you need the top of the tube 150mm below the waterline. They propose removing the water tank and fitting the thruster there, the disadvantage being you do loose some turning force moving it back. I would then need to fit a water tank in the forward section.
Ian, I would be interested in seeing photo's or more info if you have it. Especially measurements from the tube to water line.

 

[johnabbott893]

I have a MaxPower CT80 (http://www.max-power.com/Products/Electric-Tunnel-Thrusters/CT80.html) fitted to my 393 in just the space described by the OP. The fwd wall behind the heads has a panel fitted to gain access; the toilet has to be removed first.

I have 2 issues. Firstly, when I was lightly loaded I tended to get cavitation instead of thrust; this is particularly so if the fwd water tank is empty. Since going liveaboard I don't have this problem because lightly loaded is a distant memory. The second issue is thrust power. The CT80 with 65lbs of thrust will not overcome the windage with a cross wind of more than about 15kts. Still, I find it invaluable for getting in and out of some rather tight spaces that pass for marinas.

Power for the thruster is from the windlass batteries located under the fwd bunk. The whole installation is very neat.

 

[FullCircle]

Thought about one of the water jet thrusters> No tunnel, just thrust outlets to either side. Probably more hydrodynamically efficient whilst sailing too.

 

[cloud7]

I have a MaxPower CT80 (http://www.max-power.com/Products/Electric-Tunnel-Thrusters/CT80.html) fitted to my 393 in just the space described by the OP. The fwd wall behind the heads has a panel fitted to gain access; the toilet has to be removed first.

I have 2 issues. Firstly, when I was lightly loaded I tended to get cavitation instead of thrust; this is particularly so if the fwd water tank is empty. Since going liveaboard I don't have this problem because lightly loaded is a distant memory. The second issue is thrust power. The CT80 with 65lbs of thrust will not overcome the windage with a cross wind of more than about 15kts. Still, I find it invaluable for getting in and out of some rather tight spaces that pass for marinas.

Power for the thruster is from the windlass batteries located under the fwd bunk. The whole installation is very neat.

I have been trying to get info of the fitting of a thruster to a 393 for weeks , may i ask who fitted it , thks

 

[bonny]

Thanks Johnabbot893. How high up does the your CT80 protrude? Do you have a forward holding tank? Is the tunnel totally within the hull or does it extend slightly below the hull (hump)? Sorry about the forty questions but your experience is priceless.
I do have a forward holding tank (80 Litre, guess I could keep it full and smelly to reduce cavitation, SWMBO making faces!). Fitting doesn't bother me, I'm very practical and an electronics engineer by trade. Thinking of putting a battery in front of forward water tank (about 2 meters from thruster) and possibly using windlass cables to charge it. Thanks also to other members, all helps to build a picture.
Space and pocket seems to say 40 and 125mm tunnel, head saying 60 and 185 tunnel (but more chance of cavitation), SWMBO saying why bother, but refuses to take helm in close quarters. Still absorbing information, so no decision yet.

 

[johnabbott893]

How high up does the your CT80 protrude? Do you have a forward holding tank? Is the tunnel totally within the hull or does it extend slightly below the hull (hump)?

I have no fwd holding tank so there is plenty of space fwd of the head and the wet storage/hanging area. It is a few months since I was in there but the tunnel is within the hull. The bottom of the tunnel is glassed to the inside of the hull, making it as low as possible. I guess the top of the thruster is about 18" above the hull. I think the yard at Pwehellie (Welsh place however you spell it) did the installation but it may have been done by the manufactures.

Since I added a second bow anchor and 50m of 10mm chain I don't have a problem with cavitation.

 

[nickf]

I have a 393 with a fixed prop and never felt the need for a bow thruster. I note the OP has a folding prop and notes the lack of "forward braking force". Perhaps a (much)cheaper option is to consider a fixed prop. Discussions on http://groups.yahoo.com/group/beneteau393/ may be useful before making a decission.

 

[fmoran]

The last post was just about what I was going to say - get a good prop and you don't need the "addition". I have a 42 and a flexi-fold, superb control both in reverse and forward, also stopping. Got in and out of some very tight berths.

 

[Silent Lady]

The other day

Watched and helped local sailing school getting their 42ft out of a very tight berth .. Drive it forward on the spring . Back up . Reposition spring . HAve another go etc .. Bow thruster would have been far simpler ..

 

[Marsupial]

I have a 393 with a fixed prop and never felt the need for a bow thruster. I note the OP has a folding prop and notes the lack of "forward braking force". Perhaps a (much)cheaper option is to consider a fixed prop. Discussions on http://groups.yahoo.com/group/beneteau393/ may be useful before making a decission.

I have a Volvo folding prop and a much heavier boat and have no problem stopping it, perhaps the prop is too small.

As far as the bow thruster is concerned I ve sailed many years without one but was persuaded to fit one last year (its an extra crew man, you’re getting old and all of that stuff) and although I plan my approaches with a view to not using it leaving a berth sideways is a neat trick I enjoy.

 

[Martin_J]

Lewmar and QL have some good installation instructions in their guides... relating to the tunnel/tube hole cutting and fit.
www.lewmar.com/cms/assets/1/literature/200tae_thruster.pdf

www.great-water.com/pdf/QL_Manuals/Thrusters.pdf

One thing to check out that is not often mentioned is 'minimun tunnel length'. Yes, it's nice to fit as low as possible (deeper into the water).. and as far forward as possible (more turning ability).. but both of these decrease the tunnel length.

Think of having the small prop on it's own at the bow of the boat with no tunnel. It would do very little. The tunnel is more than just a way of holding the prop to the hull. Too short and reduced thrust, too long and reduced thrust and too close to the bottom of the hull and something called circulation can occur as well!

PS - Check out the hole cutting tool in the second guide. Drill a small guide hole on each side of the hull, insert the long bar.. and the cutter then looks like a router on a bearing that is slide over this guide bar.

Found it - Photos of the hole cutting tool!
http://www.great-water.com/pages/QL/Thuster/ql-06-Info.shtml
Found at this previous post...
http://www.ybw.com/forums/showthread.php?t=148621

 

[bonny]

Many thanks

Hi All,
Many thanks for all the replies. I have found a lot of them useful.
Re the Volvo folding prop. I don't think it's too small. All I know for sure is that it's 3 blade. Diameter and pitch I can'r remember. She does about 8.5 Kts at max throttle forward (flat calm Yanmar 4JH4E 54BHP) I think the problem with reverse thrust is due to the Yanmar gearbox KM35P (2.36/3.16), reverse ratio is much higher than forward such that the prop only revolves about 1/2 the speed in reverse for the same revs. This necessitates max revs to get the blades to fling out. There's plenty of forward thrust.
The jury is still out on the decision for a thruster. I've removed the panel behind the loo to access the forward holding tank (not easy as we have a heated towel rail fitted here), but as yet cant see underneath without first removing the tank (to see how much room is available) I need to replace the toilet hoses since they have rusted badly (the supposedly stainless steel reinforcing helical wire is very badly rusted, the pipe looks a dark cream colour with a rubber matt finish).
Also thanks for the advice on minumum tunnel length, this hadn't occurred to me, although I have subsequently seen this in installation guides.

 

[plato-gb]

Retractable

retractable is the way to go on a 393 from my research. For a 185mm tunnel thruster you need minimum 1/2 tunnel diameter between top of tunnel and waterline + tunnel + minimum 1/3 tunnel diameter between bottom of tunnel and hull for correct install if you're to have any chance of correct function.

This comes to 340mm. On a 393, to get this distance between waterline and hull you have to go back to forward corner of forward berth. The thruster would be too far back to be effective and you'd have to literlally lift/remove the berth to fit the tunnel.
The retractable thrusters (compact ones - Max Power 70 for instance, or Sidepower and RMC also do similar sizes) needs only 185mm between waterline and hull to be fitted.
Your distance between waterline and hull at the bulkhead behind the forward head (the one the holding tank is attached to, not the plank behind the head itself) is around 250mm so you can fit it for optimum performance behind that in the space underneath the anchor locker.
Problem we've had is that very few people seem to know (or care) about the particularity of the 393 structure. The manufacturs and their agents will tell you the equivalent of "She'll be right", take your money and then put a tunnel in your boat that is too high up and will do very little except make a lot of noise when you try to 'thrust'.
Worth noting is that one 393 owner I'm aware of has actually broken the propellers on the Sidepower 80 installed on his 393 because the tunnel is too high and floating stuff got pulled in and broke his propellers.

We have a 393 and I've been doing little else but research on this for the past couple of weeks.
pm me if you want diagrams I have collected.