Aloha

I'm brand new here and I want to post a question / start a thread about speed / range / hp, but dang if I know where to post it. It does not fit in anyplace neatly. Can you all give me a clue?
I have a 24' hull and I wish to see what would happen with different hp motors before I buy, install and run them.

 

Hi Spot
Need to give an idea of the hull shape, displacement and the desired speed if you want a meaningful answer.

Rick W

 

Aloha Rick Willoughby
Its a Hurricane h733
http://www.thewarfields.com/img/Underwater/ZodiacCutout.jpg
http://img.nauticexpo.com/pdf/repository_ne/25507/zodiac-hurricane-ribs-outboards-2518_18b.jpg

http://www.ribmagazine.com/site/index.php?option=com_content&task=view&id=148&Itemid=84
"The hull itself is a military-style deep-V (24 degree deadrise aft), monohedron type with a fine entry combined with convex forward waterlines and straight sections which provides a high level of predictability and shock-mitigation in heavy wind and sea states."

42 knots at 300 hp is what the catalog states.
What would be the speed / fuel use with a
10 hp motor, 20 hp motor and so on?

I am trying to understand the trade offs between
HP / speed / fuel consumption / range.

 

That hull shape needs lots of HP and drinks lots of fuel. You'll have to be a bit more specific about your desires or questions. A dissertation on yacht design and how it affects the various elements of powerboat design considerations isn't within the parameters of this venue. In other words, without some focus, it's a fairly broad set of subjects.

You'll probably need at least 100 HP to get it over the hump, maybe more. What do you want to do with this boat?

 

The attached curve will give you the estimated power requirement to drive the hull. Allowing for prop efficiency, leg drag and windage you typically need to double it to get close. The 300HP for 42kts is about right.

The fuel consumption will simply depend on HP if the given engines are operating near their best point. From my experience long ago this is probably around 75 to 80% of rated rpm and 50 to 60% of rated power. I have not actually looked at the fuel consumption curve for an outboard.

For example if you were happy to do 25kts as your normal cruise then a 200HP motor should work well. Top speed would be about 35kts. You need to get the fuel consumption plots for the selection of outboards to arrive at the actual consumption. The best prop selection for you cruise condition could also reduce consumption by 10%.


Rick W

 

A quick estimate suggests 5 to 6 GPH for 200 HP at 30 knots.