Bow Thruster location, Lewmar 110TT in Albin 25

[tribologist]

I got the Lewmar 110TT bow thruster and I am thinking of the install. There is room behind the tank that would be awfully elegant but it moves it back a little. Looking at the spec at a first glance:

Type: Single Prop, Blades: 5, Thrust: 62 lbs @12 VDC (2HP)
Operating Power: 12 Volts DC, Draw: 230 Amps @ 12 Volts DC 12/230A=0.0522 Ohm

"The marine cranking ampere (MCA) rating refers to the number of amperes a battery can support for 30 seconds at a temperature of 32 F until the battery voltage drops to 1.20 volts per cell, or 7.20 volts for a 12V battery."

A pair of 500 MCA batteries (my house batts) would have a internal resistance of about (12V-7.2V)/1000 = 0.0048 Ohm
5.2m AWG2 cable add .00264 Ohm so at 230A I will loose 230A * (.00264+.0048)= 1.71 Volt With some fuses and other contact resistances I'm guessing 10V to the motor so that gives me about 52 lbf.

It sounds that 50 lb is a pretty decent force and it should not matter to much if it is applied right in front of the front cabin window or up at the front of the roof?

Anyone that has a thruster installed that can give me some hints?


Added! Jim Orbans excellent instructions. viewtopic.php?f=40&t=13023

[motthediesel]

While surely it is best to mount the thruster as near the bow as possible, I doubt that a foot or so back from ideal is going to make much difference.

Our A27 came with a (Vetus) thruster, and we ran it just long enough to hear it when we bought the boat. When I tried it out in a docking situation this year it was apparent that though it made an impressive "motor running" noise, it actually provided no discernable thrust in either direction. I assumed that somehow the drive pin had been sheared off, but when we pulled the boat again after our short (launched mid-September) season, I was in for a surprise. There was in fact no shear pin in place, and the impeller was not even screwed onto the shaft. It was very lucky that we didn't lose it.

Why it was like that is a mystery -- but we're looking forward to trying it again next Spring to see what it can actually do when it's functional.

[tribologist]

Lol! Mine has the shear pin between motor and gearbox.

Apparently they use serial motors like a starter so u need to be careful running the motor unloaded

[Bob Noodat]

Lol! Mine has the shear pin between motor and gearbox.

Apparently they use serial motors like a starter so u need to be careful running the motor unloaded

Starter motors are serial? I was under the impression that they had permanent magnet stators, at least the ones that I have seen. No-load rotation is undesirable but not especially dangerous or damaging. Clarification would be greatly appreciated.

Maybe I have answered my own question, a series wound motor, found as a starter in very heavy duty industrial applications, rather than in automotive or lighter duty industrial ones:

https://top-ee.com/electric-motors/dc-m ... -dc-motor/

[tribologist]

Hmm. I cant be 100%. But there is no cogging on mine and there are 4 big ass flathead screws similar to screws holding the field coil laminations in starters. I think most “traditional” starters still have field coils.

There is also a statement in the manual not to run unloaded since it would overspeed in excess of 300%. A PM motor would typically not have a peak power that far below no load speed so i would be quite surprised if its not a serial wound motor.

[DesertAlbin736]

I suppose if you insist on a bow thruster then maybe removing the stock water tank and replacing it with a pair of smaller tanks mounted under the settees & use that bow space for the thruster might work. The replacement water tanks might have to be custom made to fit. Not knowing much about bow thrusters, but as motthediesel says locating it as close the bow as possible might be better, if for no other reason than that the "tunnel" could be made shorter and you'd have space to mount battery or batteries in the space behind where the original water tank was. Seems like cable wise it would be much easier to have a separate dedicated battery mounted close to the thruster & run short cables to the thruster and a smaller gauge charging wire from the engine alternator rather than a heavy gauge cable all the way from from your house bank. As you said the thruster would be a high amperage load but also very intermittent. Anyway, we've run our boat 600+ engine hours over the past six years in all kinds of conditions & have gotten along fine without a bow thruster so far.

[honza]

I would also consider using separate battery (batteries) not far from the thruster, which could serve as house batteries as well. Copper is expensive, the bow is too light anyway ....but big enough charging cables to get there all the amps your alternator can provide. And do not forget to account for the full length of your cables (both ways).

I would not take the MCA definition very seriously (as any of similar standards provided by the US industries - do not forget: 2 x 4 is actually 1.5 x 3.5 and shop-vac advertises 6HP....). One would have to see the exact testing procedure. Is there an ASTM test for it? You should not be running the thruster for many seconds at a time anyway. Just from my eye balling - you probably be loosing about 15% of the turning moment from the after location - which is not bad. But, is the tunnel supplied long enough?

[nebulatech]

While closing the boat up before going out of town, I took some quick measurements. I don't know much about bow thrusters, or how you will install yours, but I wanted to point out the depth from waterline of the floor in the locker behind the water tank. It is about 15" below the chine at the forward most point of the locker, which is in line with the forward end of the coach house roof.

The water line of my boat at that point is between 7" and 8" below the chine (about half way to the floor of the locker). In the attached photo you can vaguely make out my water line by looking at the pattern of chipped bottom paint. I don't know the height of the tube, or how high above the floor you would have to install it in order to glass in the underside, but my fear is that the bow thruster tube would be very close to the water line, meaning it would possibly suck air and be less effective if installed too high up.

I don't believe the water tank sits much lower than the floor of the locker behind it, maybe 2" if memory serves me. I also don't know how far below the water line the tube needs to be in order to be effective, but I'm sure the bow thruster came with some guidelines. Based purely on the waterline on my boat, it might be best to install the bow thruster tube behind the water tank, but remove the floor in the locker, as the depth of the hull increases going aft.

FWIW, the waterline on my boat was established while it sat in the water before I bought it. No anchor chain, no anchor, minimal gear, water tank probably 25% full, 650lb MD17C installed midships and a junked 30hp outboard in the rear cabin. The water line may be closer to the chine on your boat.

20201023_101111.jpg

[tribologist]

Heightwise is ok. Min is 75% of diameter to top edge. I have about 2 diameters from water line. Tunnel in package is pretty long. They actually specify a minimum tunnel length of 2 diameters and a max length of 48”. I did do the round trip in the cable calculation but im thinking it might still be a good idea to add a high MCA rated starting battery and get some more weight up front. Can run a heavy wire to the water kettle that way too!

I’ going to put it into Onshape (solid modeling tool) before cutting.

[tribologist]

Its not to crazy looking. 50 lb is decent force

[tribologist]

This is about as far fwd it can go and get it high enough over keel and long enough tunnel. Its more accessible from outside to when doing the glass work

[tribologist]

There is a perfect tank available that take 18 gal and fit behind the stock tank but its $300 plus fittings and shipping cost. Flexible tanks are sn option too

[A251975]

I installed a Lewmar 110tt in my A25 a year or 2 ago. I have written up the install along with pictures and submitted it to the Albineers of BC for their website. Don’t know if it is posted yet. A friend nearby also installed the same on his A25 and couple of months earlier. The A25 seems to have nearly ideal location for the thruster and also for the relocated water tank. The writeup shows it clearly, but measure aft from the bow along the chine 36” and lay a square along the underside of the chine and measure down 18” for the location we used. It works great off the existing starting battery...30 seconds will spin my boat 360 degrees.

[WillieC]

Dear moderators...

After reading the typo in the subject line for lo, these last how many days, could you fix it, please? I'm starting to use the word in regular conversations.

Thank you!

[nebulatech]

There is a perfect tank available that take 18 gal and fit behind the stock tank but its $300 plus fittings and shipping cost. Flexible tanks are an option too

Would you kindly provide a link? Might be handy...