Motor Height on 21' Superboat

[quicktrip]

Anyone please post motor height and setback with sportmaster lower on 21ft Superboat with 300PM. I had bad CHINE walk with the prop shaft above the pad and I was told the motor is too low. I was also told you have to learn how to drive it. So I raised the motor another inch and it got worse and the steering would get real stiff. So I lowered the motor even to the pad and it was better and somewhat drivable, if it started to bounce you could drive out of it. I then read on a v-hull you want the prop shaft below the pad, they run different than other boats. So now I lowered it so its about 1-2 inches below and it runs stable but, now the buzzer sounds and the motor cuts at @ 70mph. I checked the water pressure guage and it showed about 15psi when it happens. I was thinking ther must be a water pressure sensor on the motor hooked to the computer. It does the same thing when I jump a nice size wake. So far I have experienced the opposite of what should be expected. The fastest top speed so far is 75.1 GPS @ 5,500 rpm, there should be more mph in this set up (80+). More set back is the only thing left, I have CMC manual 6 inch jack plateand my prop is a mercury worked 28 Quicksilver. Need Help!

[150aintenuff]

first of all.. your RPM is WAY LOW... need to get her up to 6300 so decrease pitch to 24 and then get the setup right.. dont want to lug that engine.. also i would add more setback.. something totaling 12-14" on a 21 ft boat.. post a pic of the engine and pad relationship.. i would think for speeds around 75-80 you would want propshaft 2-2.5" below the pad with say a trophy or tempest propeller.. but this is all a educated guess.. maybe bash or others who have the boat will chime in with the way theirs is set up...

[quicktrip]

first of all.. your RPM is WAY LOW... need to get her up to 6300 so decrease pitch to 24 and then get the setup right.. dont want to lug that engine.. also i would add more setback.. something totaling 12-14" on a 21 ft boat.. post a pic of the engine and pad relationship.. i would think for speeds around 75-80 you would want propshaft 2-2.5" below the pad with say a trophy or tempest propeller.. but this is all a educated guess.. maybe bash or others who have the boat will chime in with the way theirs is set up...

1999 Promax 300 =6,100rpm limit , this is not a X motor

[SUPERBASH]

Only since NPartin mentioned Bash...will Bash advise quicktrip again....since Bash's wise advice to quicktrip was to rigg a 21 with a 250 fleet/torqemaster and have excellent speed/handling/driveability. Instead... hadda slap on a sportmaster 300 and now own an ever chinewalking 21 Superboat.... with warning horns.
-This is a job for EastCoastMarinePerformance. PM Bash... if you want.

[SUPAJAY]

Anyone please post motor height and setback with sportmaster lower on 21ft Superboat with 300PM. I had bad CHINE walk with the prop shaft above the pad and I was told the motor is too low. I was also told you have to learn how to drive it. So I raised the motor another inch and it got worse and the steering would get real stiff. So I lowered the motor even to the pad and it was better and somewhat drivable, if it started to bounce you could drive out of it. I then read on a v-hull you want the prop shaft below the pad, they run different than other boats. So now I lowered it so its about 1-2 inches below and it runs stable but, now the buzzer sounds and the motor cuts at @ 70mph. I checked the water pressure guage and it showed about 15psi when it happens. I was thinking ther must be a water pressure sensor on the motor hooked to the computer. It does the same thing when I jump a nice size wake. So far I have experienced the opposite of what should be expected. The fastest top speed so far is 75.1 GPS @ 5,500 rpm, there should be more mph in this set up (80+). More set back is the only thing left, I have CMC manual 6 inch jack plateand my prop is a mercury worked 28 Quicksilver. Need Help!
So you bought a 300pm, did you reinforce the transom ?? On both of my superboats i ran the prop shaft and inch and 1/2 below the pad.... but since your not running a chopper you can go lower.... you should be getting a LOT more than 5500 out of that motor... i think the revlimiter kicks in at 6100...try a 26 or 28 trophy and post your results. As for the motor cutting out i dont know what to tell you, other than to hook it up to a truck and bring it to ECM or Ocean Outboard. - Both which have the best technicians around.

[150aintenuff]

did not notice promax... soo add a pitch to my reccomendations... and get it to 6000 or so...

[blkmtrfan]

I find it very interesting that it chine walked more when the motor was higher :confused:

Do you have solid motor mounts and good steering?

When you say a 28 quicksilver are you talking about a standard merc 3-blade??

If so get that prop off the boat, they are not intended to surface....

A trophy, tempest, or even a chopper would be much better. 28p may be too much, you really want to be able to turn you max RPM at WFO, step down to a 26p or 24p

Horn when you lower your motor, and have 15psi :confused: Are you sure it is a water pressure alarm, could be low oil or something else.

I really don't think the sportsmaster is causing ill handling. It may be slowing you down at the speeds you are running comparied to a torqmaster. But it is not creating the chine walk.

[150aintenuff]

by quick silver I assume he is talking about the cheepy laser 2 or mirage copy at best... definatly not the right prop for that boat... heck they dont even run good on MY boat... I would imagine that the chine is due to the prop and case combination on that hull , the prop is slipping horrably and causing inconsistant torque on the transom which can induce side to side motions or tail wagging which can resemble chine walk in look and feel... 25 or 26 Tempest or 24 /25 trophy... get rid of that 28

75.1 MPH with a worked 28 and 5500 RPM is about 22% slip....... OUCH... GET RID OF THE PROP...

[SUPAJAY]

Lower pitch = More Rpm

[150aintenuff]

didnt you see the slip factor in his current setup.. the numbers I posted were the Info I got from his post.. in his case a lower pitch MAY NOT add RPM due to the fact that the slip is so high..

[SUPAJAY]

Very true.. 28p seems about right. He needs to take a straight edge and see exactly where his prop shaft is in relation to the pad. I also cant see why its cutting out at 70.

[amityray]

1999 Promax 300 =6,100rpm limit , this is not a X motor
My 300pm limiter kicks in around 6300-6400rpms

[150aintenuff]

that is what I thought. and he was only getting 5500 from a 28 so logically a 24 would get him to 6300.. right at the limmit... AND his current setup is 20% slip... not the right setup at all...

[quicktrip]

The prop is a mercury quicksilver over the hub chopper. It has all kinds of work done to it. I got it from some guy who riggs boats and holds some speed records. He said it should work perfect, good bow lift and cut for stern lift as well. It also has lab finish as well. The prop is not the problem I have tried a few, the 24 hit the limiter 6,100 @70 gps mph. Now the 28 should get me in the 80mph area around 6,000. I am only getting 5,500 because I cant stay in the throttle long enough between the chine walk with the shaft above the pad and when I lower the motor below the pad it doesnt chine but i get the buzzer and the motor cuts out every time I hit around 70mph on average. I have had it to 75mph with the motor high driving through the chine. Since I lowered the motor the chine walk went away but now I get the buzzer. I also had it up to 78mph gps until the buzzer sounded. usually the buzzer sounds somewhere around 70mph. it also will sound 1/2 throttle around 4k after I try to make the high speed run unsucessfull. Both temp and pressure guages read ok. What sensors are connected to the buzzer. It also was doing it when it was really ruff and i was hitting some big wakes jumping the boat out of the water (wife scared sh*t). If I can find the problem and get past the buzzer and get the boat up on the pad it will fly. I am ordering a setback, do any use the stock holes?:D

[150aintenuff]

is it a beep beep beep or a beeeeeeeeeeeeeeeeep.... if it is short YOU ARE OUT OF OIL..... long is water pressure or temp.

[150aintenuff]

STILL YOUR SLIP IS WAY TO HIGH GET A DIFFERENT PROP............ that boat SHOULD be around 10-12% not 21......

[SUPAJAY]

Try a 26 trophy, thats where i would start.

[quicktrip]

The prop has a solid hub. The prop is good, the one that came with the motor spun on the hub 1/2 mile into the water, and this latest one cost me 500$. I am not spending anymore money on a prop for now(bank is broke). I am trying to find out why the drivibility is the opposite. Motor high= porpoising and Chine. Motor low=buzzer and engine cut. The buzzer is short one second beeps untill I let of the pedal. I havent let it go past 3-4 beeps. It has plenty of oil. I was thinking at a certain speed and if i am overtrimmed could the water be passing under the pick up instead of into it?

[blkmtrfan]

I was thinking at a certain speed and if i am overtrimmed could the water be passing under the pick up instead of into it?

But you said you have 15psi when the alarm goes off :confused:



You don't have to buy your props new, check out:

http://forums.screamandfly.com/forums/forumdisplay.php?f=5

and/or ebay ;)

[150aintenuff]

CHECK YOUR OIL RESOVIOR on the engine... that beep is a low oil alarm... check for loose hoses and or fills at the remote tank... it isnt h20 presure or temp alarm.. they are constant... either it isnt oiling at all OR the float is droped down to the minimum level and it is telling you you have 10-30 min of oil left and that is why as you slow down the alarm turns off... less consumption.. less oil leaving the tank...

as for prop... it might be in perfect shape.... but it aint the right one for your boat...... hence the 21% slip........... that IS NOT THE RIGHT APPLICATION FOR THAT PROPELLER...

[quicktrip]

Oil tank is full. The response on the mechanical water pressure guage may not be instant. It only cuts out while the buzzer has its short bursts. If i keep my foot in it it will do it every other second, beep, beep, beep untill I take my foot out of it. Once I snap my foot out of it she runs fine until I wack it back down. here are some picks, the ones with the part # did not come out because of the shine.

[quicktrip]

More pics

[ghost28]

i am not a big merc guy but doesnt the alarm beep when the rev limiter kicks in...i know on my uncles cigarette it does ...and a buddy has a 250xs that he said does that too...i dunno...jus my 2 centz :confused:

[quicktrip]

Its not the rev limiter. In a hole shot I can rev it much higher and no sound. Its inconsistant some times it will do it when I hit 70 or sometimes 75mph. After slowing down it has done it a light throttle around 4k. All I do is wait a couple of seconds and try it again. Thinking about it is pissing me off. I am ready to pull the oil injection off.

[150aintenuff]

I STILL SAY OIL OIL OIL OIL OIL OIL..... make sure all the sensor wires are hooked up and tight, make sure everything is free and loose that should be and make sure you have no air in the system and that everything that is supposed to be tight is tight...

rec. RPM range to limmiter will sound alarm... constantly... overheat constantly... low WP... constantly...... oil level and oil flow... intermintant.......

[Still Crazy]

I would make two changes to your setup. The suggested setback increase to 12-14" is right on. I would however, ditch the Sportmaster in favor of a Torquemaster until such a time as your boat can exceed 85 MPH using minimal trim to carry the bow. It's an easy swap requiring only that you install shorter studs on the mid. I would also go with external steering. The Trophy is a good all around prop and handles well.

If everything is clicking and your motor is healthy, you should be in the low to mid-80's.




Still Crazy
21' Superboat
300X Promax

[SUPERBOAT21]

hello question not to get off the topic,but how do you conculate the slip factor? maybe i can see what the heck is wrong with the speed on my boat thanks jim

[150aintenuff]

OK here is the easy step by step way to calculate ZERO slip speed...

(RPM / gear ratio) * Pitch of prop = inches per minute

Inches per min. / 12 = feet per min

feet per min / 5280 = miles per min
miles per min * 60 = miles per hour theoretical top speed

1056 = (12 * 5280) / 60
simply put inches per min / 1056 = mph

MPH ACTUAL / MPH theoretical = decimal#

Decimal # * 100 = percentage of pitch value used moving hull froward

difference in that percentage # and 100 is slip.

that is STEP BY STEP that 99% of prop Slip calculators use to figure slip.. there are simplified equations out there but this never fails and can be modified for ANY combination of hull prop and power...

EXAMPLE: Actual speed 74 mph...

Given RPM 5500

Gearing 1.62

Prop 28P

5500/ 1.62 = 3395 rpm

3395*28=95061 inches per min

95061/1056= 90 MPH

74/90=.82222

100-82=18% slip


simple... but dont forget to add 1 pitch for cupping to the pitch calculations UNLESS you know the EXACT pitch of your prop...

[SUPERBOAT21]

hey thanks for explaining jim

[amityray]

http://www.boatramp.com/prop_applet/PropAnalyzerAppletG.html

Compliments of
Superbash Racing

It helped me dial in my setup!

[150aintenuff]

that calculator is based on the simple addition steps I listed.. I could have just posted all my links to different calculators I have and use but jim did ask to EXPLAINE how the slip was figured.. and with the steps I gave him he can do it ON THE WATER with a calculator that are on most cell phones and not have to wait till he gets back to the computer to check his setup changes... speeds up test setups on the water by knowing right away if the changes did anything.