215 Freedom Engine Height Adjustment

[NCFreedom]

I am posting my journey on this experiment to help others that may be experiencing similar engine mounting height issues due to additional weight being added to their boat. I have 5 group 31 batteries in the stern of my boat and a 36V 72” shaft trolling motor on the bow. I have added 8 stainless steel rod holders, tool box, spare parts, fishing gear, etc... to my boat. It is somewhere in the neighborhood of 5,200 lbs fully loaded with gear and fuel plus 3 people. The boat came with a Yamaha Saltwater Series II SS 15.5” X 17P 3 blade prop. My performance numbers are below. I have pictures of my test run after I raised the engine up one mounting hole to the third hole down from the top of the bracket. I apologize for not having the same pictures of it running before I moved it up, but you could never see the anti-ventilation plate on the outboard at WOT, or at any other speed with it trimmed up before I raised it. My original measurement from the bottom of the keel to the bottom of the anti-ventilation plate was 1/2”, after raising the outboard up one bolt hole (3/4”) the new measurement from the bottom of the keel to the bottom of the anti-ventilation plate is 1 1/4”. I think I could actually come up one more bolt hole, but I want to see how it rides in rough water and bigger waves first, before considering another move up one more bolt hole. I will probably get a 15 pitch prop as well for summer time with hotter temperatures and more people on board, as I will lose some HP in the summer. I gained 100 rpm’s and 1 mph by moving the engine up one bolt hole, it also handles better and is easier to steer at WOT. When the Anti-Ventilation plate is buried in the water(engine mounted to low), that sucks the stern of the boat down.

During my testing I tried different rpm’s and different amounts of trim to get the best performance results. The mph reading on the Yamaha gauge is always 1 mph greater than my Garmin GPS speed, so I used the GPS speeds in my test results. The spray you see coming up beside the outboard are Garmin transom mount transducers that I have mounted on both sides of the outboard. They have spray shields on them, but clearly I need to add something more to them to shield the spray more. They are mounted a little deeper than most people mount them, but it works for me, as I can read bottom depth at 48mph with no issue, other than the additional spray. I have tried moving them up so they do not spray so much, but then I lose bottom depth on plane at higher speeds.

Prop Test 2018 Yamaha F250XB Yamaha Saltwater Series II SS 15.5”X17P Date 01/16/21 Engine mounted on 3rd hole down from top

2018 Yamaha F250XB 4.2L Offshore
2018 Grady-White Freedom 215 Dual Console

3000 rpm 23mph 17% slip 3.6 mpg
3500 rpm 29mph 13% slip 3.8mpg
4000 rpm 33mph 10% slip 2.8mpg
4500 rpm 37mph 11% prop slip 2.6mpg
5000 rpm 43mph 7% slip 2.3mpg
5700 rpm 48mph 8% slip 1.9mpg
5900 rpm 48mph 10% slip 1.9 mpg

Water temp was 47F degrees and air temp was 49F degrees
2 people and 1/3 tank (30gals) of fuel