Re: 97' 4.3L v6 Mercruiser I/O Slow plane and acceleration
nickbmx25,
A few months back, I purchased a '97 Deckliner 215 with a 5.0 Mercuiser and an Alpha 1 @ 1.62 ratio. It took me about 12 to 15 seconds to get it on plane with a 3-blade, 17" pitch Solas SS prop, and the bow pointed way up to the sky before coming onto plane. My top speed on GPS ran 42 mph @ 5,000 rpm (seemed to govern out at that rpm...should run 4,400 to 4,800 at WOT), assuming the tach is correct (I haven't verified its accuracy); also, the boat tended to porpoise occasionally at WOT in both calm and wavy conditions.
The boat would get onto plane around 26 mph with a full tank of fuel and two adults. Because you are planing out at 40 mph, I would bet that you have water in the two outer sections of the hull. When I drilled holes in my haul to install tabs on the stern of the boat (tab installation described below), about 60 gallons of water drained out of each side; and, at 8 pounds per gallon, that is almost 1,000 pounds of water! The Deckliner 215 only has one drain in the center of the stern; it does not have drains in the stern on the outer hull sections, but it probably should. After draining them, I have opened them up a couple of times after boating and they do not had any water in them, but, somehow, water did get into them before (perhaps repeated waves washing over the bow and into the front anchor locker, or some section that isn't sealed).
After some research on props and trim tabs, I decided to first put on some SmartTabs (SX9510-80) a few weeks ago, and what a difference. I now pop onto plane in 5 to 6 seconds with similar weight distribution to the 12 to 15 seconds before installing the tabs! Also, the boat does not porpoise in calm or wavy conditions. The transom runs at an angle, so I could only get the actuator on the most rear-ward hole on the SmartTabs without modifying them. I now run 40 mph @ 5,000 rpm, so I am going to modify the linkage so that I can try running with the actuator in other holes to see if I can gain those 2 mph back; however, I will gladly give up 2 mph for the difference in getting on plane performance that the boat has gained. I paid about $130 for the pair of SmartTabs shipped to my door in Texas.
FYI: Check out this link for an article on a Deckliner 215 with a 4.3 Mercruiser. It shows the boat hitting 43 mph with a 19" pitch prop and trim tabs:
http://features.boats.com/boat-content/2000/08/on-deck/
Based on this article, I am going to try a 21" pitch on my 5.0 Mercruiser. I need to get my WOT down, and I also want to decrease my rpm while staying at minimum planing speed. The first prop that I will be trying is a High Five 21" pitch. I suspect that prop will work well on the tunnel v-pad Deckliner hull, and I am estimating that I will have a top speed of 46 mph with better hole shot and improved ability to maintain minimum planing speed, but I could be mistaken. I should know this weekend if my estimation is true, or not, because the prop arrives in a couple days.
