Using an Outboard Comparison site - hull weight question

[rwatson]

I am using this terrrific web site
http://outboards.findthebest.com/

for finding the best power/weight performance on a project
http://www.boatdesign.net/forums/boat-design/28ft-trailer-sailer-20-knots-under-power-51338.html


It makes it really easy to find motors that have the right HP/weight combination.



But, one of the selection options is called "Recommended Boat Weight"

What do you think the implication of that option is ?

Would using a motor on a heavier hull mean lower engine life, or what ?

For example, if the theoretical calculations show the correct HP/Engine weight figures fit, are we just talking about slower acceleration times ? or are there more insidious side effects do you think.

 

[Mr Efficiency]

A realistic assessment of what your cruise speed is going to be, would be the starting point in engine selection, imo. The actual weight difference between engines of similar hp would only be an issue if there is a peculiarity of the hull that makes it sensitive to extra weight at the stern, which would mainly be the case if the boat is relatively narrow.If your cruise speed was down around 15 knots, I would be looking at engines that turn larger diameter props than normal for the engine hp, which usually also involves greater gearbox reduction ratio. Whatever the case, the engine must be able to rev freely, well into the manufacturer's recommended range, with the propellor pitch selected. That way, regardless of the weight of the boat, you won't hurt the engine, even if the performance disappoints.

 

[Mr Efficiency]

A site like this, which has a myriad of boat/engine hp/ engine type combinations, gives a good picture of what engine suits what boat:

http://yamahaoutboards.com/owner-resources/performance-bulletins

 

[rwatson]

Thanks for that Mr E.

I had a brief scan of the prop options at
http://yamahaoutboards.com/propellers/propellers-by-application

There is plenty to think about.

In their http://yamahaoutboards.com/Marine_Rigging_Parts_Catalog/#130/z

they have the props categorized into "Recommended Boat application ( family, water sports, medium, large) ", but there is no mention of weight ranges as such.

It doesnt look like its a precise definition of any kind at this stage.