Prop for skiing

[cz_699]

I have a '63 Owens 16 foot fiberglass runabout with a 1973 Evinrude 115 Starflite (manual trim) on it. I'm looking for a prop that would help with getting a skier up, as we haven't been successful yet. Current prop is a 13x19" WOT RPM is right around 5500 rpms (tach seems accurate, but I don't know for sure, motor seems wide open), but my top speed (GPS with 3 people on board) was around 33. Boat has a new floor in it, and no water logged foam, and seems to be fairly light. I was thinking about dropping to a 17 or 15 pitch, but after seeing my rpms today I don't really want to risk over revving the motor.. I'm currently trimmed the 2nd hole out, which puts the motor pretty close to 90 degrees. Trimming it in all the way helps with hole shot, but it doesn't seem to be enough to pop up a skier.

 

[SkiDad]

at 5500 rpm you should be going about 45 mph GPS - maybe the prop hub is spun or maybe you are not running on all 4 cylinders ? Have you checked the spark with a tester - they are only about 10 bucks at autozone. I would think at 33 mph your rpm should only be about 4500

If you are trying to pull up a skier on 2 skis even a 19p should work. Now if you are talking slalom then you will probably need to drop down in pitch.

 

[jestor68]

I suggest having your tachometer checked for accuracy, because using 10% for a slip value indicates a little over 4100 rpm at 33 mph.

 

[Chris1956]

Gee, that motor should have no issue pulling a skier. Most 16 footers aren't even rated that high in HP. Check out the motor and retest.

 

[Starcraft5834]

water sports= 4 blade prop

 

[steelespike]

As suggested it is possible your tach is not accurate reading high. Slip is 33% 13% is more typical.
If the tach is off high that would account for the apparent high slip.Perhaps you can borrow a shop tach or buy an induction tach
to confirm your rpm.

 

[cz_699]

Okay, So I need to find a tach to check the accuracy of one in the boat, Check spark ( I do think it's running on all 4, it sounds pretty good, but I will verify with a tester) and mark the hub to see if the prop is spun. The motor seems to have plenty of power, but doesn't want to pop a skier out of the water very well. It seems like it drags them forever before it's possible to get up. As soon as a skier tires from being drug and not making speed the boat instantly pops up on to plane, and is up to around 25-30 in just a couple seconds. skier is off of a pylon mounted at the front of the splashwell, but we've tried to the tow eyes as well...

 

[Frank Acampora]

It may not be the fault of the engine. FIRST--we need to know: Are you trying to deepwater an experienced skier or a novice? Two Skis or slalom? Then, is the captain driver an experienced water skier or also a novice? Makes a difference because novice skiers will drag their butt way too long before getting tired and novice drivers will also make it difficult for the skier to get up. An experienced skier can "Work" the boat and pop out of the water at very low speeds. A novice dragging his but will load down almost any engine to the point where the boat will not get up and go with him behind it.

For example: I used to deepwater a slalom ski behind a 55 HP engine on a 15 foot deep vee that topped out at 25 MPH with two people and a skier. When I did slalom cuts, I could actually drag the stern of the boat around and a hard cut would put me ahead of the boat with a slack line. I never had any trouble rising out of the water--I needed to work at it but always got up, working the boat and my body. Skill and upper body strength plus good abs are necessary to ski behind a lower powered boat.

 

[Chris1956]

Frank, Whereas you are correct in your description of experience skiers and inexperienced ones, IMHO, a 115HP motor on a 16 footer, will pop a skier out of the water, even if they are a complete beginner, or they will die trying to fight that much power. I therefore suspect engine issues..

 

[kjsAZ]

Frank, Whereas you are correct in your description of experience skiers and inexperienced ones, IMHO, a 115HP motor on a 16 footer, will pop a skier out of the water, even if they are a complete beginner, or they will die trying to fight that much power. I therefore suspect engine issues..

+1 to that! My last boat was a super heavy 17.5ft deep-V boat with a very tired 90HP 6-in-line outboard and I had zero problems to pull my Admiral up the first time she tried to water ski. With 2 adults and 3 kids on board it ran 35mph (GPS).

With a 16ft and a 115HP inexperienced skiers should have a problem to hold on when he takes off. And with 3 on board it should run a lot faster than his 33mph.

 

[Maclin]

For example: I used to deepwater a slalom ski behind a 55 HP engine on a 15 foot deep vee that topped out at 25 MPH with two people and a skier. When I did slalom cuts, I could actually drag the stern of the boat around and a hard cut would put me ahead of the boat with a slack line. I never had any trouble rising out of the water--I needed to work at it but always got up, working the boat and my body. Skill and upper body strength plus good abs are necessary to ski behind a lower powered boat.

Wow Frank, I had this same experience, all technque (and a big flat long ski!). I had a 15 foot tri-hull with 55hp outboard (both Chrysler) with your same top speed, had a good time once I got the process down. Had to limit the payload to just me and the driver because I weighed about 250 at that time. I think that prop as an 11p.

Friend around that time had a 115 Merc on a 19footer I think, and I did not need to use as much technique, came right up. No idea on the prop but that boat could get well past 40mph with just he and I in it.

 

[Maclin]

...and If i was on 2 (big flat long) skis behind the 55hp it popped me right up.

 

[cz_699]

I wouldn't say any party involved is "experienced" for skiing, but I can at least get up on skis behind an inboard ski boat. Some one with a whole bunch of low powered skiing experience could probably get up behind it, but I've only "almost made it up" after fighting behind the boat for several hundred feet. I haven't had a chance to try anything out yet diagnostically, I live in a resort town, so the lake is jam packed this weekend. If I get a chance I'll try early tomorrow, otherwise it'll be some morning next week. I picked up an OMC 13 3/4 x 17" stainless prop because I couldn't refuse the price, but it won't be here until mid next week.

 

[cz_699]

Induction tach should be here tomorrow, 17p prop on Thursday. 19p is marked to check for being spun. I'll probably take the boat out in the AM (before the tach gets here) and find out if the 19p is spun at all. Then Friday AM should get real numbers for both a 17p stainless and the 19p aluminum thats on it.