What to doo ?

[2even]

I have a 1985 Wellcraft Scarab Sport with twin counter roating 225 Evenrudes 1989. The props are OMC 14 1/4 x 21. I can only get 4000 aprox. rpm at WOT and it takes a long time to plane. Can anyone tell me if this seems like a prop problem or something else ?

 

[Mark42]

Re: What to doo ?

Did it just start happening or has it always been this way?

 

[2even]

Re: What to doo ?

The boat was rebuilt over a long period of time some five years. I have never used the boat untill recently. I have been thru the motor repair section and have hit a dead end. I personaly cannot believe that props are the problem. This week I plan on borrowing a pair of 14 1/2 x 19 from a friend of my brother to see if there is a difference. Is there a site that can advise as to what size and type of prop to use for a certain set-up.

 

[gatorred]

Re: What to doo ?

how long gas been in it,if sat for long time it might bad. this will play a trick on you to if over looked

 

[Ron G]

Re: What to doo ?

Every boat and hull are different and so are props,so one maybe good on one boatand engine and another on the next,start here there's, lots of great guys here that have more Knowledge on things then most will learn in a lifetime.I wish i could help more but i don't anything about twins or saltwater boats.

 

[Dhadley]

Re: What to doo ?

This is indeed a 30' Sport, not the 26' Sprint, right? <br /><br />Are the motors transom mounted or bracket mounted? When parallel, where are the AV plates in relation to the hull?

 

[2even]

Re: What to doo ?

The fuel is new, clean.The carbs all re-built and double checked with wire,air and airesol. The timing was set as per Joe reeves and compression was between 80-90 with no more than 7-8% difference on any bank. Hi Dhadley you helped with the carbs on a previous post. The motors are on a transom mounted bracket, the av plates are about 1" above the hull. The right motor on the starboard and the counter rotating on the port.How can I post pictures of the setup.The boat is a 30' SPORT.

 

[Dhadley]

Re: What to doo ?

OK. I'd guess that 21's are a bit optimistic on that boat especially with the motors mounted that low (real low). Before I started changing props though I'd sure play with the height. <br /><br />Now that you have the boat in the water, lets check the timing with a timing light. Just to make sure. I do it the same way Joe does but we always double check it.

 

[Dhadley]

Re: What to doo ?

One more thing while I'm thinking about it -- how's the toe set? In or straight or out? How much?

 

[2even]

Re: What to doo ?

Dhadley I am assuming when you refer to the AV plates you mean the cavitation plates on the motors?. As far as the toe they are just a bit out if looking from the rear. Is there any way that I can give you a call to talk over these problems.<br />As allways I appreciate all the help.

 

[Dhadley]

Re: What to doo ?

The plates are commonly called cavitation plates although they do nothing to promote cavitation. They actually help prevent ventilation so they are, technically, anti-ventilation plates. AV for short. We need to know where they are in relation to the hull directly in front of each motor. That will be the X dimension. Since yours are 1" high you have a 1" X dimension. The brackets are probably about 28" or so long. That means the X dimension could be about 5-6".<br /><br />As for toe in or out, it's just like your car. Standing in back of the motors looking forward at them, on a V bottom you want them toed in slightly. IE -- the nose of the gearcase (toe) in slightly and the propshafts (heels) out or away from each other slightly. 1/8" to 3/8" should be fine on that boat.

 

[2even]

Re: What to doo ?

Dhadley, since we are talking about the same item you are correct. The bracket is 28" and the motors are toed in slightly have not measured but I beleive it is within your measurements. Just a thought would jack plates help and if so how high do I need to go as the motors are as high as possible as they are now mounted. I have some pictures that I took this morning, just don't know how to post.

 

[Dhadley]

Re: What to doo ?

If we're as high as we can go and the plates are still only an inch up we'll probably need manual jackplates. Not uncommon. I like Bob's Machine plates because you can use them in the 2.5" setback configuration. You have all the setback you need with the brackets. Naturally there's nothing saying you can't use the full 5" setback though.

 

[2even]

Re: What to doo ?

If I use jack plates, with the info provided how high do you think I need to go to achive WOT in the correct range using the props that I have. I also have seen the fixed type that will give me anywere from 3" to 5.5", what about these.

 

[Dhadley]

Re: What to doo ?

I'd say that 3 - 5" is going to do it. Manual plates have about 6" of travel. However, I'm not sure jackplates will get us all of the 2000 rpm we're looking for but they sure cant hurt. I think you'll need them for the correct set up no matter what props we end up with.

 

[2even]

Re: What to doo ?

Dhadley, here in Miami we are having a marine flea market at which I was luckey to get a pair of new Hi-Jacker plates at a bargain. I also will be borrowing a pair of 14.5 x 17 s/s props to test the set-up. I made a mistake in the bracket set back, it is not 28" but 24" does this matter?.<br />Probably will not be able to test this weekend but as soon as I have tested will post results.

 

[Dhadley]

Re: What to doo ?

The setback is OK at 24". You just might not be able to tilt the motors without hitting the transom in some cases. Sounds good. Keep us informed!

 

[2even]

Re: What to doo ?

I have mounted the jack plates that only gave me 4" of lift with 6" of setback. I am going to test this afternoon with the props that I have, also will be carrying a set of 14.5 x 17 aluminum, 14.5 x 19 s/s, 14.25 x 23 s/s 4 blade. I was able to borrow these just incase to see the different results. I will post results as soon as I return.

 

[2even]

Re: What to doo ?

Dhadley, the setback allows me clearing the transom. Also I set the jackplates to max height for the test.

 

[Dhadley]

Re: What to doo ?

Sounds good! Keep us posted!