Bow thruster location

[Lietuvis]

Hello

Im naval engineering student and im curently writing dissertation about bow thrusters. My task is to chose bow thruster for small tanker (yeah i know this forum is not about this type of "boats" ).

"Safety requirements dictate that it must be located behind the collision bulkhead."

I dont understan from what point of view it means behind collision bulkhead. Bow thruster should be located behind collision bulkhead closer to stern or behind colison closer to forebody (bow)?

Hope you understand what i wanted to ask, im not perfect at english

[gonzo]

Behind is not a nautical term. It should indicate aft or forward of the bulkhead.

[Lurvio]

Could it mean an enclosed, watertight compartment?

Just a guess.
Lurvio

[micspoko]

Almost always bow thruster is behind a collision bulkhead to fore (bow) and seperate compartment to have acces in different situations and for watertight. Closer to the bow it is better

[Lietuvis]

So is it good decision to place thruster very close to bow (at forepeak tank)? Thruster diamater is 0,9 m and width in targeted area is about 1,3 m, so there is not many space.

Alternative choise is to instal thruster at station near 0,1 L as shown in picture. But in this case transverese bullhead should be cut to slide thruster into hull. And tunnel lenght at that location is very long too (about 4D) which means more resistance and less thrust. Also im not sure classification societies and rules alow to cut vital bulkheads.

I find very anoying and quite dificult to find proper decision for tunnel placing

[micspoko]

I think the best choice is on 0,1L but the bow thruster must be lower then you show in double bottom. When you do in forpeak you have to lot to do to build a separate watertight space. When you cut out a bulkhead and insert a thick tube with the appropriate longitudinal stiffnes then you will have adequate strength

[Lietuvis]

I think height is OK, becouse bottom immersion should be not less than one duct diameter measured from duct axis to keel (some sources say it should be not less than 1,5 D).

But if i install thruster close to bow (in water balast tank as mentioned earlyer), suck all water from water balast tank and don't build watertight space to thruster?
Becouse of hole (tunnel) in hull there is some displacement loss + weight of the thruster (~500 kg pluss weight from tunnel extension) will probably replace or even exceed wieght of the balast water so stability should be fine. Or maiby some rules dictate that i can't "touch" balast water?

Also i forgot to mention that thruster is hydraulic drive and pipes goes from thruster to pump room in stern.

[micspoko]

You should have possibilities to flooding a forepeak because it will be special condition do this - for example maybe it is need when docking to dry dock. For height a bow thruster - in this year we do a conversion a 70m ship and install a new bow and stern thruster. On stern thruster was 80mm(this dimension is not a mistake) above keel and bow thruster was be about 300mm above keel - diameter tube 1500mm. All was accepted by Germanish Lloyd
This is a small vessel and when he operate without cargo the bow thruster may have too small immersion to do a job

[Lietuvis]

hmmm...
draught is 3,6 m
waterline area at that location ~380 cubic metres
gross tonnage 300 t
and tank capacity 320 cubic metres

as i understand, acording to these characteristics, draught wihout cargo will be about 2,6 metres (one metre smaller than original). At that draught thruster still be submerged more than 1D from waterline to duct axis, which is minimum depth acording to warious recomendations. i think In good weather conditions its enought (don't know about bad ones )
Anyway, if i install thruster deeper should i cut double botom at the tunnel location and veld thruster into it, or i should cut double botom and create small watertight compartment for the thruster?

[micspoko]

How much is DWT(only when you know this can be assumed draught without cargo). The GT is a volume of hull with superstructure.
I thing the best way is do a watertight compartment with acces from main deck .

When ship is without cargo have some trim and draught on the bow is smaller then you calculate

[Lietuvis]

DWt is 600 t, and probably you are right about draught.

Is instaliation as shown in picture OK? I also thinking of conical hull fairing, becouse waterline angle is wide at tunnel axis, so i left more space for it.

[micspoko]

I think this is the best solution for this ship

[Lietuvis]

Ok, probably i'll stick with it. Thank you for help