Adventures with my '88 250 EC

Today's adventure involved a new prop.  I had three props to try that were borrowed from the local prop shop called pro-pellers.  I was looking at three factors, slip% at cruise, holeshot time to plane, and finally top speed. 

This boat is new to me this season.  I have done the following to the engine: MSD 6M-2L with a drop in distributor, A stock vortec ignition coil from a 1999 4.3L Chevy.  The lower unit is a 1.5 ratio alpha one, but we are going to a same ratio bravo one at end of season, the alpha is simply too sloppy and it is worn out.  The carb is in good shape with only needing a choke level adjustment.

First let's go over the current 15.25 15p 3 blade aluminum.  It had to be filed recently after it suffered some gravel damage,  It was still in working order and has been sent out to become back backup.  The holeshot was terrible and the top speed was 32mph with full tank and 3 adults at the engine maximum rpm of 5200. 

Next, at the prop shop recommendation we put the elephant ear 16x16 aluminum 3 blade on, it barely cleared the anode and was the worst of the group to holeshot.  The top speed was 35.5 mph at 4600rpm, slip according to the math was less than 10% at full throttle.  This prop had an unusually high cruise fuel consumption around 12 gph at 27-29 mph. 

The second new prop I tried was a Solas Amita 3 E- Plus 15.5 17p 3 blade aluminum.  It was slow out of the hole, a little boggy on the motor, it didn't like slow cruising but had the best top speed at 40.5mph @ the full 5200 rpm.  It cruised well with 10.5 to 11 gph fuel consumption at 29 mph. 

The last prop was a Solas Amita 4 14.5 x 17p aluminum prop from their heavier cast line.  It was the smallest physical prop but had 4 blades going for it.  This prop  required anode trimming, I didn't know that at the time and had to take the anode off to complete the test (I ended up not having issues without the counter rotation trim) This was far and away the most responsive prop.  It was small enough to still slow troll at 2 mph or so but the holeshot was nearly immediate.  I feel confident using this prop to pull skiers out of the water with such a large boat (no easy feat im sure, and we will test it).  Holeshot was half the time of the 16x16, around 6-7 seconds to go from just above idle 5-6 mph to on plane.  The cruise fuel consumption at 29mph was worse than the amita 3, around 11.2 to 11.5 gph.  However it had the most stable slow on plane cruising, the best turning, the best holeshot and it had enough slip coming out of the hole to get into the powerband immediately.  Cruise slip was very very good, under 10% but I feel the efficiency (fuel consumption hurts it the faster you go.  Top speed was 39.5 mph at 5200rpm.  I think the boat could run a 14.5 x 19p 4 blade and shift some of the inefficiency towards the top end where I tend to spend less time. 

I have kept the Solas Amita 4, a competitor makes the same prop in a 15.25x17p, given what I know about diameters now, If you increase diameter a heavy boat will not be able to get a 4 blade into the powerband for a quick hole shot. 

I will try the 14.5x19p 4 blade progressive the prop shop makes on Sunday.  I didn't have the hub adapter for it at the time so it was excluded from the test. 

Again thanks for the wealth of information on this forum as I continue to find adventure with the Rinker, I thought I would share my tests and experiences with it.  On a side note, people at the sand bar were baffled I changed my prop three times in an hour.