What kind of speed should I expect out of my boat?

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darthvegagt

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« on: May 05, 2010, 09:48:44 PM »
I have a 1983 Omega 20' open bow I/O with a SBC in it. Bought it a couple months back and its my first boat. I'm just curious as to how fast I should expect this boat to go? Im not at all out for speed, but I feel it should go faster than what it goes at the moment. I GPS'd it at 36mph going up river out at Fisher's Landing.

When I first got the boat it ran like crap from bad plug wires and such. So I tore into the motor and put a Summit hydraulic cam and lifters in it (282 duration with .465 lift), new true roller timing chain, a Weiand Single plane intake and 650 Edelbrock carb was put back on. Also put brand new HEI dist. with new wires and plugs. The motor runs great in my opinion. The boat has a brand new 14X21 pitch SS prop on it that came on the boat when I bought it. It has a Mercruiser Alpha One series one outdrive.

Is thinking that my boat should go closer to 50 mph wrong? Is a dual plane intake better for my boat? One issue that I haven't gotten to yet it that the tach isn't working so I'm unsure as to what the motor revs to at wide open. I have used some of the online prop calculators but am unsure about a few things. I don't know the drive gear ratio....I just used 1.84? I don't know the RPM the motor is turning.....so I just put 4500? and I don't know the prop slip %.....so I used 12%?

Am I pissing in the wind? lol ??? ;)



darthvegagt

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« Reply #1 on: May 05, 2010, 09:53:33 PM »
This is my boat....

crewchief22

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« Reply #2 on: May 05, 2010, 09:59:33 PM »

Am I pissing in the wind? lol ??? ;)


The first problem is most of the guys here don't know much about i/o's and really don't want to.

GT is going to be your best source of information and he should chime in soon.

The cam specs seem a little off to me, most 280 series cams have around 480 lift.  I think you would have a better combination with a dual plane intake manifold (like an Edelbrock Performer RPM) than the single plane for the cam you have.

Good luck and welcome to SCJB
  • Boat #1: '77 Hondo Pantera GT Jet
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« Reply #3 on: May 05, 2010, 10:18:24 PM »
My psychicly
predicted answer from GT.  ;D

 Fix your tach, we need to know what rpm the motor is turning.

 
Welcome to the club of broken boats :o  Pay here$ bend over and move along.

darthvegagt

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« Reply #4 on: May 05, 2010, 10:21:36 PM »
Thanks I'll have to get his opinion. Hopefully he sees this thread ;D

I actually have a Performer intake which is why I asked. I think it probably would be better too since my boat doesn't have so much done to the motor nor is it a top end boat.

As for the cam, the specs state 282/292 duration with .465/.488 lift. Maybe my motor combo is wrong....not sure

I plan on hooking up a tach and running it this sunday to get a baseline.

76 Bonneville

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« Reply #5 on: May 05, 2010, 10:51:09 PM »
Small block with a prop should be in the mid 50's.
Diffinently need to know what rpm's you're running, something aint right.

darthvegagt

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« Reply #6 on: May 07, 2010, 09:23:46 AM »
Bonneville,

That's exactly what I was thinking. I feel like its just not going the speed it should. Im planning on taking the boat out this weekend with a tach ;D so I'll let you guys know.
Thanks again for the response, check back in a few days and Ill post the results.

Jordan

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« Reply #7 on: May 08, 2010, 07:12:45 PM »
I took the boat out today and here's the results.

With the SS prop (14x21 pitch) the boat RPM to 4500 and went 35 mph at wide open throttle.

With the old prop (14x19 pitch) the boat RPM to 5000 and went 36.5 mph.

I think the boat may need to have the carb gone through and possibly even a bigger carb. My brother has a Holley 650 double pumper I am thinking about trying. Right now the boat has a 600 or 650 Edelbrock (can't remember what it is right now).

Any ideas or thoughts as to how I can get this thing to go faster?? ???

crewchief22

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« Reply #8 on: May 08, 2010, 09:48:54 PM »
Have you checked for water saturation under the floor?  It could easily be a couple hundered pounds more than it is supposed to be.

In the picture it sure looks to be setting deep in the water.

 
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« Reply #9 on: May 09, 2010, 01:28:10 AM »
from how you describe it, it doesnt sound like the engines running out of rpms or power though. maybe the out drives geared incorrectly, because those numbers are wayyyy low. One of my best friends has a 28 foot pontoon boat that stays out at the river, and even though i know pontoon boats dont weigh hardly anything, with the stock 350 in it, we got it to do 46 at about 4500 rpms after we tuned it up a few weeks ago. If ur getting 4500 rpms, but only getting 36 mph, somethings not right. I would check for extra weight like crew chief said.

GT Jets

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« Reply #10 on: May 09, 2010, 01:39:37 AM »
Just got home from work and can't sleep...Saw the thread and think you have more than one problem...

Is this a Mercruiser or an Obsolete Marine Corporation deal?

I feel you have a bad torque coupling or a bad propeller hub and this causes a major slippage not unlike a slipping clutch in a car. The problem I have with blaming the prop is you have tried two different ones.... :screwy:

Second, providing you have a 350 Chevy/260 HP Merc, the ratio should be 1.50:1, you should also be running in the 4200-4500 rpm range with a 21" pitch prop...If your getting 5K, that is one good running SBC....

If you feel the tachometer is even close, leave the carburetor alone...

Three questions..
1. Do you know how to properly trim the boat out? You need to trim the drive "up" while under way and get the hull out of the water, if left "down" it will plow like an icebreaker and not perform worth poo.  :thumbdown:  When trimming the drive, while on plane trim up until the hull starts to porpoise, then bring it in (or "down") a tick, this will be the optimum point for top end performance...

2. How much crap/people did you have in the boat? The load needs to be proper to ensure a sound center of gravity...

3. Have you weighed the boat and trailer?...A water logged hull will make you chase your own butt... :-\


My last Alpha I (Merc) boat had a 260 HP 350 with some mild mods including a square bore carb, a 1" carb spacer (4 hole), a dual plane intake, through transom exhaust and a giant hillbilly flame arrestor and it could do 65 MPH at 5000 rpm all day with a Quicksilver High Five 21" pitch wheel.

You should be able to get into the low 50's without much fuss... ;)

GT
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

darthvegagt

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« Reply #11 on: May 09, 2010, 01:04:59 PM »
ok so what and where is a torque coupling? I tried looking up what it is and even looking at parts drawings of the outdrive to no avail.

My boat has a Mercruiser Alpha one series one outdrive.

I have no problems taking the boat to get weighed but what should the boat and trailer weigh in at?

I have ran the boat with only me and a cooler and gotten 35mph with the 21 pitch prop, yesterday it ran 34mph (same prop) but I had myself and 3 other people in it. So not much of a difference in speed to me.

I think I need to atleast take the carb apart and clean it out for the peace of mind that it all in order. I was told that the "prop hub" was the inner part of the prop being pressed into the bladed part of the prop with a rubber seal, sort of like a harmonic balancer. Is this right? because both my props look good and I cannot tell where they would be pressed in etc.

As far as the water saturation, I don't think that is a problem, I can look into the anchor storage compartment and there is no water to be hiding anywhere.

The trimming part I have been doing wrong and been leaving the drive in the down position (my first boat what can I say ;) ) I can try what you mentioned the next time I go out and see what it changes.

In the meantime, I'd like to look into the torque coupler and prop hub stuff if you can give me some better understanding of how to check that. Thanks for all your guys help. I want this boat to do what its supposed to. And no one wants a Pontoon to blow by them on the water.  :P LOL

GT Jets

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« Reply #12 on: May 09, 2010, 01:28:12 PM »
The torque coupler iss attatched to the crankshaft of the engine at the flywheel...Annual alignments are necessary to keep it from failing...

Trimming the boat out should be worth 10-15 MPH... :thumbup:

GT
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

darthvegagt

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« Reply #13 on: May 09, 2010, 01:40:06 PM »
10-15 really? holy moly....blame it on the driver then...haha

So everything is so cramped towards the back of the boat that Im not sure if I can see the coupler. Is it rubber? I suspect I would need to pull the motor to even check or replace the coupler?
I can see the shaft coming out from the flywheel to the outdrive and looks like a round (maybe rubber?) coupler thing. Not sure if that is what you are talking about.

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« Reply #14 on: May 09, 2010, 02:05:58 PM »
10-15 really? holy moly....blame it on the driver then...haha

So everything is so cramped towards the back of the boat that Im not sure if I can see the coupler. Is it rubber? I suspect I would need to pull the motor to even check or replace the coupler?
I can see the shaft coming out from the flywheel to the outdrive and looks like a round (maybe rubber?) coupler thing. Not sure if that is what you are talking about.


You cannot see the torque coupler...It is inside the flywheel cover...

You need to retest with your new found trimming skills  >:D

GT
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

darthvegagt

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« Reply #15 on: May 09, 2010, 02:17:51 PM »
roger that!....I'll update you when I try it out....thanks again.

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« Reply #16 on: May 09, 2010, 03:17:24 PM »
TRIM IS GOOD .  .  .  words to live by
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darthvegagt

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« Reply #17 on: May 10, 2010, 04:43:20 PM »
So I took the boat out again this afternoon....

The trim did help some, with the 19 pitch prop the boat went 40 mph at 5200rpm. I put the 21 pitch prop on, bimini down, took out anything that didn't need to be in the boat (chairs, cooler, etc) and the boat went 43 mph at 4600 rpm down river. If I could get the boat to rev to 5200 or so with the 21 pitch prop I'm sure Id be in the 50's.

In the midst of all this I ended up towing a 26ft Pontoon boat the had the water pump go out in it. lol

So whats your thoughts on speed etc? Should I swap the intake to a Edelbrock Performer? Try a holley 750 vacuum? I have those sitting at my brothers. Or you think the coupler is bad?

GT Jets

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« Reply #18 on: May 10, 2010, 08:06:09 PM »
So I took the boat out again this afternoon....

The trim did help some, with the 19 pitch prop the boat went 40 mph at 5200rpm. I put the 21 pitch prop on, bimini down, took out anything that didn't need to be in the boat (chairs, cooler, etc) and the boat went 43 mph at 4600 rpm down river. If I could get the boat to rev to 5200 or so with the 21 pitch prop I'm sure Id be in the 50's.

In the midst of all this I ended up towing a 26ft Pontoon boat the had the water pump go out in it. lol

So whats your thoughts on speed etc? Should I swap the intake to a Edelbrock Performer? Try a holley 750 vacuum? I have those sitting at my brothers. Or you think the coupler is bad?



Propeller slippage is out of control...(excess of 25%)   :thumbdown: :thumbdown:

The easiest way to check a torque coupler is to put a breaker bar on the front crank bolt of the engine and put the outdrive in reverse gear then stand on the prop in a forward motion (don't cut your leg off) engine off obviously, there should be no rotation of the prop (I do not think this is your problem....)..........

You either have a serious hull deflection in the bottom, a ridiculous hook, or your GPS or tachometer are full of shit.... :-\

You should be in the high 50's (58.2 AT 7% slip) with a 21" prop and a 1.50:1 gear ratio at 4600 RPM....Something is amiss.

GT
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

darthvegagt

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« Reply #19 on: May 10, 2010, 09:42:58 PM »
GT,

Im going to check the torque coupler like you said tomorrow. Im not sure about how to really check deflection. I am also going to get a string line and 4 ft level to check the hook in the boat.

As far as the GPS and tach, Im pretty confident that they are correct. I'm starting to think I should take the boat to Keith at the boat shop here and have him look at it to see if he can narrow it down, but hoping I can figure things out myself so the boat isn't in the shop.

More to come tomorrow.....thanks.... :banghead:

darthvegagt

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« Reply #20 on: May 11, 2010, 06:28:50 PM »
checked the torque coupler like you said. I cant stand and push on the prop and sucker doesn't budge. Haven't checked the deflection or hook yet though....


 


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