I have a prop problem

[eliminator1974]

I have a 97 Daytona 25' with a 565 BB an 1071 blower with a super chiller. It has a bravo 1 lower 1.5 ratio with imco upgrade shafts and a 2" shorty lower. The boat came with a 28 pitch prop and it ran good but it spun the motor up to 6500 rpms. So we tried changing props to a 32 pitch prop (lab finished) to get the rpm down without losing any mph. But the problem is with this 32 prop at 3000 rpm it will not go on plane. At any rpm over that the prop cavitates and of corse the motor revs up. Can anyone give me some help. The boat was still slow to plane with the 28 pitch prop.

[gmocnik]

a lot depends on where the drive is setup to begin with...i have the same boat, quad rotored 540..950-1000 hp. the top of the transom assembly is about two inches below the rub rail. i turn 1:32 gears and a 32 inch non-labbed bravo..
i tried a two inch shorty and could not roll the boat over without blowing out the prop....tried a five blade 30p hering...no help...
i put hydraulic sponson tabs on the boat to help the 60-70 mph poproise (did not really help that) and i put those all the way down if i really want to get one plane without any bow rise...boat rolls over very easily at 2500 rpm
i say ditch the 2 inch shorty....sounds like the x dimension is high....

[Phat Matt]

Do you have tabs?

[Dave C]

ya measure the X-dimension and report back..

[eliminator1974]

please tell me in detail how to measure the X dimension? Thanks

[Dave C]

from bottom of boat to center of lower unit of drive (i.e. in line with propshaft)
Has anyone tried a drive spacer?
Maybe by increasing the x-dimension you can get the boat to stop cavitating. I've never tried one so I dunno.

[eliminator1974]

The measurment is 6 an 3/4 of a inch with the lower unit in full downward postion.

[buzzaro]

You didnt mention what type of prop or props they were. Did you change the type of prop you were running, # of blades, diameter of blades etc? These things could make a big difference also.

[eliminator1974]

both props are bravo one props (lab finish) 4 blade

[Dave C]

I will go look at mine tonight and let you know the difference. We can see how high you are.
The measurment is 6 an 3/4 of a inch with the lower
unit in full downward postion.

[eliminator1974]

Thanks I would very greatful. :)

[2forcefull]

what rpms are wanting the boat to turn? why didn't you try a 30p
a 30p you would go faster at less rpms. what rpm did you spin the 32?

[eliminator1974]

With a 28 we spun 6500rpm and i wanted to lower that into the 5800-6200 rpm. When I talkd to our local eliminator dealer he told me to use a 32 or 34 pitch prop. so I tried the 32 pitch prop an I cant the boat to go on plane. :cry:

[DMOORE]

It sounds like the 2" shortys may not be giving the drive enough leverage to get the boat on step. There are drive spacers available that go from 1/4"- 2". My boat runs a very high x dimension with sportmasters, and I have to roll the throttles on nice and steady or the props can slip getting on step. BTW did the boat originally have the short lowers on it from the factory?
Darrell.

[2forcefull]

With a 28 we spun 6500rpm and i wanted to lower that into the 5800-6200 rpm. When I talkd to our local eliminator dealer he told me to use a 32 or 34 pitch prop. so I tried the 32 pitch prop an I cant the boat to go on plane. :cry:
try the easy way first, if you got on plane with the 28p then you can get on plane! a 30p prop should get you to 6100, figuring 200 rpms per 1pitch----what's the wheel size?

[eliminator1974]

this boat ran 118 with 1.5 gears , 28 pitch prop, and this 2 inch imco shorty. we just rebuilt the motor, added an intercooler and have picked up about 250 horsepower over what was there before. we are now between 1100 and 1200. this is a 2 step hull and never has a problem with porpose or chine walk or any other nasty habits. it just flat runs. we are trying to get a bunch more speed out of the boat. the eliminator dealer said to run 32 or 34 pitch prop with the shorty and drop the drive ratio to 1.25 or 1.3 to keep the revs down at lower speed but also to let us hit big numbers at upper revs. i just spent over 10,000 on the rebuild and really don't want to dump a bunch of money in trim tabs just to get on plane when the boat doesn't need them any where else. i also don't want to have to buy a whole new lower unless it is an absolute.the 30 prop really won't give me the big top end that i am ultimately looking for. both of these props are 15 in in diameter. we bought the boat used . this boat used to belong to 'pleasantcat'. sometime i will go with an imco extreme or similar drive but right now i am just trying to get some breakin time on the new motor before the ice comes.(it was 47 degrees on the water today !!! just because the custom pistons have taken 8 weeks to get here !

[h2oski2fast]

this boat ran 118 with 1.5 gears , 28 pitch prop, and this 2 inch imco shorty. we just rebuilt the motor, added an intercooler and have picked up about 250 horsepower over what was there before. we are now between 1100 and 1200. this is a 2 step hull and never has a problem with porpose or chine walk or any other nasty habits. it just flat runs. we are trying to get a bunch more speed out of the boat. the eliminator dealer said to run 32 or 34 pitch prop with the shorty and drop the drive ratio to 1.25 or 1.3 to keep the revs down at lower speed but also to let us hit big numbers at upper revs. i just spent over 10,000 on the rebuild and really don't want to dump a bunch of money in trim tabs just to get on plane when the boat doesn't need them any where else. i also don't want to have to buy a whole new lower unless it is an absolute.the 30 prop really won't give me the big top end that i am ultimately looking for. both of these props are 15 in in diameter. we bought the boat used . this boat used to belong to 'pleasantcat'. sometime i will go with an imco extreme or similar drive but right now i am just trying to get some breakin time on the new motor before the ice comes.(it was 47 degrees on the water today !!! just because the custom pistons have taken 8 weeks to get here !
After doing the math I don't see how that speed could be achieved without having a slip percentage of about 2% (highly unlikely), or unless the motor is spinning 7300 rpm with a slip of around 8%.
Was the prop labbed by Merc or a prop shop?

[eliminator1974]

sorry for the lack of info. you are correct in your math. pleasasntcat used some 5 bladed prop and was turning 6700rpm when he gps 118.he sold the boat and it ended up at lake cumberland marine. when we got the boat it had a 28 pitch bravo. i don't know what happened to the other prop or if it got on plane with ease or great difficulty. i do know that who ever was the last one that rebuilt the motor before we got it did a backyard job. we had to replace everything except the block and crank because of garbage. wrong size bolts had been used. the deck was uneven on the block and the pistons were actually smacking the head. in order to save the block we had to have custom pistons made which is why it took all summer to get them plus a screw up on making them. at one time it looks like the motor had been built right but it wasn't when we got it. i missed all of the poker runs this summer including running to havasu (already had reservations ) due to this motor. this is why i really wanted to wait until next year to replace the drive or any other major project. i have very few days !! to get the boat in the water here as we just had our first frost last night. i am trying to get the boat broke in so i can at least make a fast trip down to cumberland in a week or 2 before i put the boat up for a long winter. i have only had this boat in the water a total of 4 times- 3 in early ,early , cold spring when i got the boat for shake down test runs, and once yesterday after the rebuild.

[Dave C]

the problem as I see it from your description is that it blows the prop off while you are getting on plane... no bueno.
While you are trying to get on plane can you feather the throttle and will the RPM's got up and down as you do this? If so, thats no good.

[DMOORE]

I've seen the problem with other boats before. What it sounds like is happening is, the smaller prop is able to hook up coming on plane , even though there is a very high x dimension. The problem occures when you try to use too much pitch on the prop and it will not "bite" . This same thing can occure on big offshore boats also. Basically there are 3 things you can try.
1) Call the manufacturer and find out which prop they used. A 5 blade will loose a tiny bit of top speed, but it will hook up better out of the hole. Most likely why they had it on before.
2) Install a drive spacer. This may be the best solution because I think the drive might be too high to begin with.
3) Install trim tabs. Although many large offshore boats need them to get on plane, it would most likely be a bandaid for something not set up right on a boat your size. But it would most likely help.
Darrell.

[eliminator1974]

thanks for the advice. i am going to put the 28 pitch back on just so i can get some break in on the motor. i will probably try the spacer rather than the trim tabs. i also feel that it is really not the right fix for this boat although it might be a last resort to get going and go fast. i have a set on another eliminator v bottom that chine walks at 85 even with the tabs. that boat also has a built 565 but it is not blown. thanks dave

[HavasuDreamin']

Where in Indiana are you? I am in Indianapolis and have a 19' Daytona. If you are at all close, we should hook up next year.
HD

[eliminator1974]

I live in Kokomo, In. U can give me a call sometime, my number is 765-860-0532

[Dave C]

ditto.
I say #2 then #1....only cuz the spacers are cheap.
see what you can beg borrow and steal to test and tune.
I will try to remember to measure the x dimension tonight before I start drinking :rollside: :rollside:
I've seen the problem with other boats before. What it sounds like is happening is, the smaller prop is able to hook up coming on plane , even though there is a very high x dimension. The problem occures when you try to use too much pitch on the prop and it will not "bite" . This same thing can occure on big offshore boats also. Basically there are 3 things you can try.
1) Call the manufacturer and find out which prop they used. A 5 blade will loose a tiny bit of top speed, but it will hook up better out of the hole. Most likely why they had it on before.
2) Install a drive spacer. This may be the best solution because I think the drive might be too high to begin with.
3) Install trim tabs. Although many large offshore boats need them to get on plane, it would most likely be a bandaid for something not set up right on a boat your size. But it would most likely help.
Darrell.

[don johnson]

Do you have an extension box? If not that would probably be perfect with the shorty lower? It will move the prop back and into clean water which should stop you from blowing out the prop.
If an extension box is not an option and you are set on keeping the 2" shorty, tabs would help a bunch coming on plane. Not only will they push the nose over but when they are extended down they will channel water towards the prop which should help in keeping the prop bit. Once on plane, bring them up and away you go...

[RiverDave]

The measurment is 6 an 3/4 of a inch with the lower unit in full downward postion.
Eliminator1974, I just skimmed the thread so somebody else may have already addressed this.. The measurement is how far the center of the lower unit (where the center of the prop shaft would be) above or below the center sponson of your Elim. That's the X dimension (vertical) Not how far away from the center sponson it is.. (easily confused from what was described above)
I'm not too well informed on X - dimensions and where they should be, just trying to clarify how you measure it.
I've never had to measure one before, but I imagine the easy way to do it would be to put the drive in the down position.. Take a tape measure and measure the center sponson to the ground. Then measure from the ground to the center of the prop shaft (making sure the thrust angle is parrallel to the bottom of the boat, as well as the bottom of the boat is parrallel to the ground). The difference between the 2 #'s should give you your X dimension height either above or below the center sponson.
RD

[HavasuDreamin']

...I will call you sometime...especially if I am hitting Salamonie or Missisenewa (sp?).
With regards to your boat, if you haven't already done so, a conversation with Pleasantcat might give you a baseline of how the boat performed when he owned it.
Good Luck.

[h2oski2fast]

Eliminator1974, I just skimmed the thread so somebody else may have already addressed this.. The measurement is how far the center of the lower unit (where the center of the prop shaft would be) above or below the center sponson of your Elim. That's the X dimension (vertical) Not how far away from the center sponson it is.. (easily confused from what was described above)
I'm not too well informed on X - dimensions and where they should be, just trying to clarify how you measure it.
I've never had to measure one before, but I imagine the easy way to do it would be to put the drive in the down position.. Take a tape measure and measure the center sponson to the ground. Then measure from the ground to the center of the prop shaft (making sure the thrust angle is parrallel to the bottom of the boat, as well as the bottom of the boat is parrallel to the ground). The difference between the 2 #'s should give you your X dimension height either above or below the center sponson.
RD
What if the ground isnt level?

[Dave C]

or use a straight edge on the center sponson....
Mine was 5.75"
we have different hulls and motors so I dunno how much this is going to help you.