Outboard Thrust Rating (better than HP?)

[toneusa]

I've been looking for the amount of thrust provided by small outboards. Can't find any info other than calculations. Seems to me the pounds of thrust would give a more accurate rating of efficiency than the engineers horsepower rating. <br />15-20 years ago Practical Sailor bought several outboards in the 10hp class and tested the lbs thrust. BIG DIFFERENCE !! seems like 30% variation in 10 hp motors. 60% or 70% when in reverse.<br />I haven't found any info at the manufactureres sites.<br />Does anybody have any solid testing reports for 5 to 10 hp outboards? 2 stroke or 4. A simple test will do. Tied to the dock pulling against the same fish scale.<br /><br />Thanks <br />PS the reason I'm asking: the one that came with my 27' sailboat, did not perform the first time I needed to stop (didn't even slow it down with all sails down). I'm looking for max thrust at max RPM's, forward and reverse, 10hp and under. I'm looking for someones real life comparisons, not calulations.

 

[G DANE]

Re: Outboard Thrust Rating (better than HP?)

The reason this mesuring hasnt been used since was it could only tell very little of what the motors actually perform. Tie your boat to the dock and pull, and you will know which motor pulls best at aro 1500 to 2000 rpm. Often this will be the same motor that gives you the lowest top and cruising speed, compared to others of same size, as this is something quite different. Hp mesured at prop tells you how much work a motor can do for you with the correct prop for your boat. It is true accelerating to this speed dosnt take exactly the same time from all motors, but ?

 

[novacane]

Re: Outboard Thrust Rating (better than HP?)

do they put out torque ratings for outboards<br /> many engines can be close it hp but very qiute differantly in torque and what rpm its <br />maxed at. hmm just a thought

 

[toneusa]

Re: Outboard Thrust Rating (better than HP?)

Outboard thrust...just seems to me that is the bottom line in determining performance. do they all measure hp at the prop? car engines are at the fly wheel with considerable, variable loss at wheels. torque?? depends on prop and true hp=thrust. do they measure hp or calculate it? it still seems to me measuring thrust at cruise or max rpm would be the true equalizer for performance especially if they included reverse.<br /><br />Would anybody get ticked off if I reposted same question in hopes of hearing from an engineer or manufacturer?

 

[sloopy]

Re: Outboard Thrust Rating (better than HP?)

the propello is not as effeciat at reverse

 

[Lugnut36]

Re: Outboard Thrust Rating (better than HP?)

Remember horsepower is directly related to torque and rpm it is a simple measure of how much work an engine can do over time at a given rpm (usually optimal) 1 horsepower = 33,000 foot pounds of work in 1 minute. Propping etc has nothing to do with engines ability to do work. It's like taking two identical cars and one has 4.11 rear end gears and the other has 3.73, obviously the car with 4.11 gears has more pulling power at low end and acceleration but the car with 3.73 rear end has more top speed ( different example of tying your boat to a dock theory ). But yet their engines are identical in horse power!

 

[Bear]

Re: Outboard Thrust Rating (better than HP?)

Hi Tone!<br /><br />Have you read this?<br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=17;t=006933

 

[orca]

Re: Outboard Thrust Rating (better than HP?)

G'day. A question that I have asked before on this forum but have not yet had a satisfactory answer is, Why are outboards not marketed using cubic capicity as a selling tool? Motorbikes are sold usinc CC, 500CC. 750CC etc. Ask any teenage boy and they will tell you the cubic capicity of the latest model cars yet outboard manafacturers seem to keep cubic capacity in the small print on the brochure. There is a big variation in cubic caoicity of outboards, for instance the Yam 70Hp is smaller in capacity than the Merc 40. Does this mean that the merc is poor because they can only get 40HP from 930CC or is the yam going to fail because they squeeze 70HP out of a motor that is only about 850CC???

 

[orca]

Re: Outboard Thrust Rating (better than HP?)

G'day. A question that I have asked before on this forum but have not yet had a satisfactory answer is, Why are outboards not marketed using cubic capicity as a selling tool? Motorbikes are sold usinc CC, 500CC. 750CC etc. Ask any teenage boy and they will tell you the cubic capicity of the latest model cars yet outboard manafacturers seem to keep cubic capacity in the small print on the brochure. There is a big variation in cubic caoicity of outboards, for instance the Yam 70Hp is smaller in capacity than the Merc 40. Does this mean that the merc is poor because they can only get 40HP from 930CC or is the yam going to fail because they squeeze 70HP out of a motor that is only about 850CC???

 

[Bear]

Re: Outboard Thrust Rating (better than HP?)

Hi Whaley!<br /><br />I saw that one before. I posted the same question/thoughts in our swedish forum some time ago. I have a Kawasaki 80 (750 cc/80HP) and a Honda 800 (50HP/800 cc) The other way around look a bit funny. That sure goes for cars too.<br /><br />What you are asking is why HP is so important for outboard manufacturers. I think that has to do with max HP ratings for different boats, insurance, power limits in some lakes and so on. <br />Another difference is that a car or motorcycle are built as a complete "unit". Boats are made for a variety of engines and power. The buyer's needs and choice. Both for new boats and when it's time to new engine for the old boat. <br /><br />In Sweden the insurence companies use a power to weight ratio to determine how much the motorcycle insurence will cost. Motorcycle manufacturer still use cylinder volyme in the model name <br /><br />As there is no torque figures for outboards the cylinder volume should absolutly be of some concern too. Who look in to that when it's time for buy a nem one?<br /><br />Well, a bit off topic in this post but that was my thoughts.