Prop shaft 4" below the bottom, 153 cubes, and can't pull a 125 lb. skier??

[Ron V]

OK guys, between my father, friends, and me, we've got a few decades of tinkering with boats of various types, though admittedly not with this much power. This one has us beat.

My Rapid Craft was built as a SKI boat, and they were used by ski clubs. Plain old rounded v-bottom with strakes. The boat has a 23" transom, so I know they are able to run at least that high and pull skiers. I have the motor about 1/2" above the transom (2nd set of holes). This puts the prop shaft about 3.5" - 4" below the bottom when tucked under. No setback. People who have seen my boat run know that there is nothing wrong with the setup for top speed or cruising.

The problem: I've tried skiing behind it, and it's real strong for the first 10 feet or so, until the boat breaks over. Then the prop lets go. It does this when I'm just riding too - but it's not much of a problem, just part of getting a high performance rig on plane. It's even OK with passengers. But put a load behind the boat and it can't handle it. It just sits and spins. It's worth noting that I am actually up out of the water and the ski is on plane when the trouble starts, so obviously it is having a very difficult time with even minimal load on it. The prop is not biting AT ALL apparently. I'm a 125 lb. skier starting from deep water on a 65" slalom ski.

This happened with the 27" SRX, so I thought a thru-hub would solve it. Put on a 27" Laser II, - it was worse! Almost blew the rods out of the motor. Bought plugs for all three vent holes on the Laser II and it didn't help the blowout on a normal takeoff (in fact it hurt the initial holeshot) with no skier, so I don't want to try pulling a skier again with it. By now I'm thinking it's a problem with that much pitch just not being able to bite with that little forward speed. So, just for kicks, I put the 21" cupped 2-blade bronze inline-6 prop from my dad's boat on it and took it out just to see how it would bite with no load behind it. Not sure if the smaller diameter contributed to it, but it almost didn't get on plane with just me in it. Herein however may lie an indication that there is an inherent problem with turbulence with this rig if a prop with fewer blades and less cup had more trouble?? So....three different props, three different designs (granted it was a joke to try the 2-blade bronze), with a 6" variance in pitch, same inherent problem. Funny thing is the overhub prop (SRX) had the least trouble.

The boat runs 72 mph with a stock 150, but as it sits I'm not confident it would pull an 175 lb. person on an inner tube. Something is grossly but very simply amiss, what I don't know. Maybe a 21" High Five with triple-cupped blades? The motor height is fairly conservative......there simply HAS to be a way to get the power to the water. :confused:

[Raceman]

I believe it's just the transom height. I put a 1500XS on my 18' Sidewinder once. It was a 15 " motor on a 20 " transom with no setback and no notch in the bottom. It wouldn't get on top with a through hub SS round ear similar to today's Mirages, and I finally screamed it on top with a chopper. Your motor is probably about an inch lower than that one was.


Easiest thing to do is put a jackplate on it so you can lower it to ski.

[Earl Murchison]

Large cavitation plate . Try to get the bow a little lower before you give it the gas . Good luck.

[Bruster]

You might want to try a 5 blade High Five. Keep the pitch down 22-23" so you have more pulling power. I can ski behind my 20" transom 15' Avenger with 15" 1500XS mounted flat on the back with one :eek: .

[T-REX]

Hey Freeky, see if U kan find a "Shooter" prop...I have one on my big REX, and it will plane wit me, or 6 people...no matter...It will also take off trimmed down, or trimmed up, and never looses bite....I think your problem iz PROP!!...Tru U have tried several wit the same results, but az they say, 2 WRONGS DON'T MAKE A RITE!!....so try'in 4 props wit the same charatristikz don't help the problem...GIT WIT A GOOD PROP MAN THAT WILL WORK WIT YA!!...Good luck...REX

[pyro]

Lower-pitched props tend to ventilate less as they fall on plane. Nobody needs to use a 27p for skiing. A 19, 21 or 23 would be ideal.

[Rickracer]

:D ....and the addition of something like a Bob's MJ-5 would help too. http://rickracers.com/product_info.php?cPath=50_120&products_id=35 With 5.5" of setback, all the way down, you should have no problems getting on plane with even a bigger skiier, and jacked up, it might even help your top speed. If 5.5" is too much setback, you can bolt it together as a 2" setback, and/or 6* wedge for more tuck. Maximum setup flexibility. Your cost would be $179 + shipping. :cool:

[1BadAction]

ahhh, its just all that mad merc HP... :D

[RUDERIOT]

with his responce----try a Shooter . A small one 21-23''

[Tom D.]

I agree on the prop. I had a Checkmate Enchanter and used to run a 24 chopper . That thing would slip alot till you got on plane with no skier. When we went sking I changed my prop to a 15X20 4 blade cleaver. No slip at all and rip the arms off of skiers :) . Wouldn't go fast at all and I had to watch the rpm's. But it was for sking and did't have or need to go to fast. 10 min. change for night and day.

Tom

[150aintenuff]

21 p high 5 or rev 4 will bite to ski... try a revolution 4 with 2 open plugs and 2 solid...

[Hydrasports205]

5-blade's are sweet for pullin skiers....Rex thinks a lot of his shooter...don't have any experience with one yet, but I might pick one up soon.


I had a 21p high five that kicked ass for pullin skiers or cruisin.

[hsbob]

only thing i woold add to the 21" highcupped prop is a set of doel fins. when you tuck the motor under they act like trim tabs forcing the bow up. they also widen the cavitation plate area which may help.

[captcarb]

The ski club probably ran a 25 inch motor jacked an inch or a little more. I rarely see a ski club boat with more that 17 inch pitch no matter how many motors were on it. They often run 15's on the OMC's. I have never seen a ski club boat with the cav plate much above the bottom of the boat. They don't need anything above 45-50 mph, but they need a lot of snap and thrust. If you do get it up on plane it will probably ventilate like mad in the turns.


I can pull a bunch of skiers with my 150.

Jim

[supercat]

Just a quick thought, My brother had a ski boat with a 150 on the back. He was using a tall pylon to attach the ski rope to. The added leverage from the tall pylon when the boat tried to roll over on plane was noticable. If you are using a tall pylon to clear the powerhead, try a lower attach-point just to see what happens.

[hsbob]

if you want the best pull. get a land and sea shifting prop. at 11-13 starting pitch it equals a tourmant boat for pull. then let it shift to 19 -21 for economy during the ski pull. do not ....do not surface perice this prop.


only problem is the cost of the prop. used ones are out there.

[brotherxb03]

You can't pull a skier with a 27 pitch prop with a 150 unless you have it on a 500 lb boat or sheet of plywood dude!

[Ron V]

It's got plenty of power, just not the bite. If I could get it to hook up, it would do it with a 30. No beer gut and really good at getting up on slalom, that's the secret. I'm actually up when it lets go.