40% efficiency gain from dual prop bow thruster?

[Chris1956]

I read an article in BoatUS Magazine on bow thrusters. Their claim was that dual prop thrusters had 40% more thrust for the same wattage, as single prop thrusters. The 40% loss in the single prop thruster was because of the power needed to spin the water. Sounds like crap to me.

Anyone have any analysis?

 

[Scott Danforth]

dual props are more efficient than single props. in both bow thrusters and outdrives

 

[Texasmark]

I had one of the high thrust Minn Kota bow mounted trolling motors I bought new in '89. Problem with long blades (which it had....13" dia as I recall) for high thrust is getting them turning especially at lower speeds. Yeah verily you have that long "moment arm" for thrust, but you have to get it going first. If you are bassin and working a bank you want off and on corrections in spurts to keep you lined up and the big, long, 2 eared single blade just didn't get it. I have seen other motors (Motorguide as I recall) with a single 4 short blade design which should work pretty good. I would have to look at a two prop to voice an opinion. My last was a single prop Motorguide with 2 blades with a length about 2 1/2" and 57# of thrust on 24 volts. It worked really nice. Thing is, if you look at the power consumption curves if you stay in the lower region of the unit's power rating, the efficiency is much better. It's a logarithmic curve and gets real steep at the high power end. So just get a big motor and run it slow.

If you are talking about a lateral thrust mechanism that has a propeller in a tube mounted in the bow of the boat then I have no idea.

Mark

 

[Chris1956]

Mark, I was discussing Bow Thrusters. They come in portable models as well as ones built into the hull at the bow.

 

[Texasmark]

Sorta thought that was a different critter due to the terminology you used but I didn't know they made them portable also.

Mark

 

[Chris1956]

Bump to top.

I was expecting someone to chime in. I my mind a dual prop bow thruster is analogous to a VP dual prop or Bravo Dual prop. I have never heard that those dual prop outdrive were more efficient than single blades. I have heard the dual prop outdrives handle better.