12 foot v-hull won't plane

[Court_Dallas]

I have a 1978 Starcraft 12 foot v-hull. I have a brand new Mercury 9.9 on the back, but my little boat still won't quite get on plane. I have it trimmed all the way down but it still porpoises and doesn't plane off. I have thought about modifications that might help but was hoping someone out there has dealt with a similar issue and will share what worked for them.

Any thoughts?

Thanks.

Court

 

[bunnymoney]

50 years ago I had a 12 foot alumacraft with an early 50's 10 HP Mercury Super Lightning . It didn't porpoise, but didn't really stay in the water either. On one occasion I crossed many wakes in the river. The boat popped into the air and promptly barrel rolled to an inverted position on the river. Kerplunk.
It was fast and dangerous.



If your 12' porpoises it is on plane, just not the plane you want to be on. Is your 9.9 a long or short shaft? Is your 12 footer a 15 or 20 inch transom? They need to match for the best operation.

Set the prop shaft parallel to the bottom of the hull. From this point your comfort will be determined by adjusting the location of whatever else is in the boat, i.e. fuel tank, passengers, coolers and other gear. This should be simple and probably go close to 30mph which is pretty scary in a 12 footer. Wear your PFD.

 

[ezmobee]

Long shaft motor on a short transom was my guess as well. A 9.9 should plane a 12' just fine unless you weight 900 pounds

 

[Watermann]

Your little tinny should plane fine with a 9.9hp unless as mentioned it's a longshaft on a 15" transom then it will have a bunch of drag. Porpoising can be worked on with the weight moved more toward the bow, if nothing else grab a lighter weight buddy that doesn't tip the scales over 200 and add him towards the bow.

A 9.9 on a 12'r will top out on a plane around 18 - 19 mph.

 

[bunnymoney]

??? Was your 9.9 sold as a "kicker" model with a very low pitch 4 blade prop?