Author Topic: scale bollard pull  (Read 2581 times)

0 Members and 1 Guest are viewing this topic.

skibo

  • Newbie
  • *
  • Posts: 11
scale bollard pull
« on: June 07, 2016, 19:15:04 »
Hi I haven't been on this site for a long time, DON'T worry I'm not a spammer!
I have been doing other things for the last couple years, some of it building and sailing r/c sailboats. I have had a couple tugs before, my last one was the Bugsier 3 by Gurapner, I'm starting another tugboat from scratch and it'll be in 1/24 scale or half inch to the foot of a 120 foot ocean going tug. My tug is 60" long and 17" beam and I figure a 6.5" to 8" draft. I am wondering how to make a scale bollard pull indicator to find out which motor and drive I can use to get the most power from. I have several type motors, I have 2  geared 2.7.5 Astro 25s  and 2 Mubutchi 950 series motors with a 5.1 gear set up. I also have 2- 1/4 hp 12 volt large fan motors New, but only turn around 6500 rpm that could be used with the 5.1 gear drive. I  have two different types of props to use, 4" 4 blade and a 5" 4 blade props. I don't know if I'll make hoops for the props or not. The reason for a bollard pull test is which combination to use without tearing one set up out of the boat to try another, if I could bench test them it would save a bundle of time and work. I don't know, maybe I'm just digging in too deep here and getting to complicated, but I live in Southwest Washington State close to the Columbia River and I would like to run it in the river, but it will need a lot of power especially at tide change or ship/tug wakes! This is the reason for the questions. I figured I would build a small test tank and a barge like boat and mount one set up in it at a time in it instead of the tug it's self. Any help here would be of great value.
skibo

west coast tug

  • Sr. Member
  • ****
  • Posts: 298
Re: scale bollard pull
« Reply #1 on: June 08, 2016, 20:39:37 »
From the tug size your planning a car battery for power.
Try and spin the props at about 2500 RPM out of the water. With a Ballard pull of 6-8 Lbs from each prop that's if your going twin screw.
Displacement of being heavy in the water is your friend , Some fellows make the tugs too light .Sounds like your going to be about 150 Lbs.
A good combing inside the house for water tight.Keep the house low don't make it super tall stability problems start to add up quickly
Try the 950's first , You will have to get a good quality Speed Controller about 30 amps each  .
If your not a twin screw tug a bow thrust-er will be a good idea .
Re guards to a test tank if its not large enough the water will circle around  and give you false readings .A trip to a small lake is better.
As for the nozzles ,Yes they add a lot to the power of towing .
If your making it a steerable nozzle  your maneuvering will be better  for docking only not much different at the power pull .
I build a lot of river towing tugs nozzles are pointed down at 13 degrees and are pigeon toed 10 degrees out ward , These tugs are short hulls your ocean towing will have the shafts straight to the keel and level to the hull bottom ( Max thrust aft )
Gary

skibo

  • Newbie
  • *
  • Posts: 11
Re: scale bollard pull
« Reply #2 on: June 09, 2016, 08:02:03 »
Thanks Gary, I don't plan on steerable nozzles, I figure either fixed or I might run without the nozzles, haven't made up my mind yet. My tug will have a rather large super structure in keeping with the plans I have, I'm planning for it to be much lighter than the hull was constructed. I think the 950s with a 3-1 gearing will get me the best results, I'm a little slow right now on working on my boat as I'm suffering from some back trouble. I will try to get some pics. of the hull in it's early stages here shortly. Thanks for your reply to my question.
skibo

plJeffrey2

  • Newbie
  • *
  • Posts: 2
scale bollard pull
« Reply #3 on: February 16, 2017, 04:00:18 »
Hi all do you guy z now of any shops in london that i can get some scale 600 models  got a freind  who says hi want to send me some please let me now thanks

C-10

  • Sr. Member
  • ****
  • Posts: 342
Re: scale bollard pull
« Reply #4 on: February 16, 2017, 14:13:35 »
Hi ....... built "Big Bertha" [see modern tugs] 54in by 18in with 2 steerable nozzles and 95mm props from the prop shop who advised me to keep below 2000rpm  and expected a Bollard Pull of 24 lbs. Kort nozzles were expected to give an extra 30% on a static pull but decreased as the vessel got under way due to the korts water resistance and in some cases gave a minus percentage pull at full speed.

 Hope his helps............Pompyboy 
« Last Edit: February 16, 2017, 14:17:18 by C-10 »

Volker

  • Sr. Member
  • ****
  • Posts: 337
Re: scale bollard pull
« Reply #5 on: February 17, 2017, 01:32:59 »
Kort nozzles increase the propeller thrust but produce a higher resistance. At about 10 kn the higher resistance equals the thrust increase.

You get the highest bollard pull when the tug is fixed to the shore. When the tug is towing an object the bollard pull is usually less, as the moving object doesn't need as much power.

Additionally the power available for towing decreases when the tug is moving as the tug needs part of the power to move its own weight.

A tug with kort nozzles has a higher bollard pull but a lower free running speed than the same tug without kort nozzles.
Regards, Volker