bollard thrust is indeed a pull test and can be a valid comparison of boat (as in tugs "I can push a bigger barge") or propeller performance (My prop is better than yours when used with motor xyz and ratio 123). It is not a measure of motor performance unless the exact same propeller from the same manufacturer is used on all motors in the comparison. You should also be aware that simply specifying diameter, pitch and number of blades of the prop would not be sufficient to give accurate data. Thrust is more closely related to blade area and shape. Normal propeller specifications do not have sufficient information to make using a bollard test a valid comparison for motors. Until there is a standard propeller then the bollard cannot be used for motor comparison between manufacturers.
If you want to swap motors and compare how the motors worked in your exact application then bollard thrust will work because the same prop is being used.
Hp is one of the most confusing specifications in the world in theroetical science it is exact. However in practice every engine and motor manufacturer plays a numbers game trying to get the highest possible rating on the nameplate. (i have played the name plate spec game I know that often what is on the plate is the highest tested rating they could get under ideal labratory conditions and Consequentially I don't trust any rating very much (it is called a safety factor)) usually somewhere in the deep dark recesses of the spec sheets there is a second or even third number that is more realistic. For an ic it is usually continuous rating at some rpm in electrics it is usually found by sorting through the derating factors.
Try getting some of the newer ISO spec sheets from your suppliers at least some of the specifications are getting closer to real life.
larry
--- In electricboats@yahoogroups.com, Joe Siudzinski <siudzinski@...> wrote:
>
>
> On Aug 24, 2010, at 22:44, redu wrote:
> >
> > Weird specs!
> >
> (snip)
> > They should say:
> >> Cruise 4.0 R thrust is comparable with 9,9 hp gas outboard thrust at
> > boat speed of 0 m/s.<
> > This is possible, as propeller is better, and el-motor thrust is good
> > at low rpm.
>
> This thrust number is referred to as the "Bollard Pull Test" and is
> usually applied to tugs. For my cruising boat, I am interested in this
> zero-velocity thrust figure (unobtainable from outboard manufacturers)
> because I'd like to know against what sort of wind loading (separate
> topic) I can still try to make forward progress, or, especially,
> maneuver inside a marina when it's blowing.
>
> For my 9.9hp Yamaha Hi-Thrust outboard (the 323cc not the 232cc
> version), I measured around 250#. These outboards have significantly
> higher thrust than 'conventional' 9.9hp outboards.
>
> http://www.katiekat.net/Cruise/KatieKat2003E.html#050503
>
> Having the static thrust number from Torqeedo (214# for the Cruise
> 4.0R) allows an apples-to-apples comparison and for me is quite
> acceptable if I wish to replace the Yamaha. Wish all outboard
> manufacturers did this.
>
> JoeS.
>
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