Ideal depth of prop/ surface peircing props

[Sonnie00]

Hi guys,

Thanks for the help choosing an engine for my 11' Whaler. I now have a 25 hp longshaft. from the bottom of transom to the top of prop is about 11". I am having trouble getting boat to plane w/two people in it. (w/just me it goes like stink!)

I am planning to use an aluminum plate to raise the engine and so get the prop higher. What is the ideal depth of prop? What are the advantages of making make the prop "surface-peircing"?(Other than being able to tell people that I have a surface peircing prop)

Any help for the future setup greatly appreciated.

Thanks, Andre.

[nevd]

Hello Andre,

Have a look at Motor Position Armstrong Bracket thread - this should give you some ideas.

Also do a search as there have been a number of recent posts on similar subjects in boatdesign.net - eg "Outboard bracket help".

Regards,

nevd

[John David]

People in small boar racing (10 to 12 feet) claim surface piercing, although helping at racing speeds, actually reduces thrust required to get over the "hump". Try moving youself and your passenger as far forward as possible when starting out, in order to get the cg in a better initial trim. Of course once the boat planes you can both move further back.

A long shaft engine may put the center of thrust low enough to exacerbate the high bow problem, so raising the engine up can't hurt,even without surface piercing.