My best pass

[88workcar]

I have a 1980 14R Allison, I run a homemade 14" 90 Yamaha 3 cyl. My best pass ever was two weeks ago with a 26-27 merc cleaver, 7100 rpm @ 79.5 mph. My previous best had been 77mph for quite a while. I have been doing a lot of set up work, very little changes at a time and it payed off. I did go out to duplicate the run and have not done it again. My attempts fell short at 78.3 last Sat, and 77.2 on Sun. The conditions were worse that weekend. My goal is a solid 80mph. I will not try to go any faster, it is too much for my hull, and I would rather not tear it up.

[zul8tr]

Most difficult to get repeated results. Many variables: water temp (changes viscosity thus drag), air temp (air drag and engine power), water surface wave and current condition, humidity, wind direction, engine A/F ratio for the conditions present, ign. timing, spark plugs, overall weight, etc. ......

Good luck on the 80 mark. Keep in mind water density is over 780 times greater than air density therefore water drag for the same conditions is a very important item and every attemp to reduce it is a plus in speed.

http://www.theweatherprediction.com/habyhints/216/

BTW what is the condition of the bottom planning area: high gloss?, waxed?, coated with anything?, sanded dull in water running direction with 600 grit?, rear edge sharp rather than rounded to shed off water clean rather then have surface tension cause water creep up the transom and pull the rear down?, sharp edges on the fore-aft lifting strakes on the bottom for clean side relief of water spray?, etc?.....

I run my hydro with a 600 grit sanded bottom, very sharp rear trailing edge on the rear and sponsons planning surface.

Jim Russel has a lot of performance tips for download

http://www.aeromarineresearch.com/about.html