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 Post subject: Cannot get on plane
PostPosted: 08 Aug 2016, 14:27 

Joined: 08 Aug 2016, 13:31
Posts: 10
Hi everyone, I have been running this little 16' aluminum boat for a few weeks now. It has been running pretty strong since i have had it, but i recently started really opening it up (more than 1/2 throttle). The issue is that it has only really gotten on plane once, took a few seconds (about 10) then i got it up to 28 MPH at 5200RPM, and dropped it to 24MPH 4800RPM. This was with fishing gear cooler, 10gal of gas, and just me in the boat. The very next weekend, i got out with same conditions, but add my son (100lbs) and the boat tops out at 14 and does not hit plane. In both cases the trim was set to the same location, same fuel mixture, same weather and conditions. I tried having him sit up front but that did not help. I brought it home after putting around fishing all day and checked it all out Carbs, plugs, plug wires, lower oil, fuel, fuel filter, exhaust port in lower is free of carbon build up. No new noises, or know issues that would have caused it to drop top speed.

Took it out again this morning got it up to about 20 mph to check and see if i spun my prop (both marks were lined up same as i left them). boat ran top speed of 20 with just me no gear. again no noises.

I am thinking it might be either an ignition problem (plug wires) or maybe a prop issue. Either way i have done a bit or trouble shooting, and i know that this boat should be getting up at least past 20mph and on plane no problem with all gear and me and my son(100lbs). tonight i am checking compression on all cylinders, and spark to all them, might buy a new set of plug wires.

SPECS for boat & motor:
older 16' side console mod v
1989 Mercury 50hp outboard (classic)
prop - 11.1"x13" solas
3/8 marine decking
live well
under decking foam is dry (not water logged)
bimini top
new plugs, lower gear oil, recent carb cleaning on both carbs, new fuel filter.

any experts out there have any first hand experience with this let me know what you think i should be able to run with my set up, and or good troubleshooting advice i am all ears.


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 Post subject: Cannot get on plane
PostPosted: 08 Aug 2016, 14:34 

Joined: 08 Aug 2016, 13:31
Posts: 10
Just ran a few calculators and saw that with my prop i have on now i should be hitting 27 WOT. I am consistently running 17-20mph WOT, is this a combination of weight, and prop issue? or is it a engine issue?

1989 mercury 50 hp 2 stroke (classic)

HP/Model WOT RPM Gear Ratio
50 Classic 5000-5500 1.83

Propeller Pitch - 13
Gear Ratio - 1.83
Engine RPM - 5300
Actual Speed (MPH) - 27
Propeller Slip - 25%


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 Post subject: Cannot get on plane
PostPosted: 08 Aug 2016, 19:17 
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Joined: 15 May 2010, 00:38
Posts: 2399
Location: Central Florida
Before you go pouring money into parts you are not sure you need why not tuck the motor in farther against the transom and run again.
Anytime you add weight you may need to trim in to get it on plane.
Also, not quite sure here. You indicated you have run @ 28mph at 5200 one time. Is it capable of that now with the same load you ran it at?
You also stated 20mph but no RPM. Was that at WOT? Same trim angle? More information we have the more accurate feedback you will recieve.


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 Post subject: Cannot get on plane
PostPosted: 08 Aug 2016, 20:51 

Joined: 08 Aug 2016, 13:31
Posts: 10
Pappy wrote:
Before you go pouring money into parts you are not sure you need why not tuck the motor in farther against the transom and run again.
Anytime you add weight you may need to trim in to get it on plane.
Also, not quite sure here. You indicated you have run @ 28mph at 5200 one time. Is it capable of that now with the same load you ran it at?
You also stated 20mph but no RPM. Was that at WOT? Same trim angle? More information we have the more accurate feedback you will receive.


The motor is a manual trim, and has been ran in the same location every time i have had it out, 3rd hole from the transom (6 total).
I believe it is capable of running 28 consistently. The issue is it has been running 18-20 MPH and wont go past that.
The weight has not changed much only one extra person, my son who weighs 100 lbs.


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 Post subject: Cannot get on plane
PostPosted: 09 Aug 2016, 00:27 
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Joined: 15 May 2010, 00:38
Posts: 2399
Location: Central Florida
Okay.....reading comprehension here. Answer the direct questions I have asked and let's go from there?
I do not care that the engine has been in the same trim pin hole the entire time. You have made changes to the boat (I took the liberty of reading your identical post in Boathouse). With any change in weight and weight distribution the engine trim usually has to change. Not only that but the 3rd pin hole from the transom is pretty far back, specially for an engine that is not known for good bottom end horsepower and torque. You are the one asking for help and suggestions here. Answering that the trim pin has always been in the same location is a bit argumentative. There are some very knowledgeable folks in here that can help if you let them.


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 Post subject: Cannot get on plane
PostPosted: 09 Aug 2016, 07:09 

Joined: 08 Aug 2016, 13:31
Posts: 10
Pappy wrote:
Okay.....reading comprehension here. Answer the direct questions I have asked and let's go from there?
I do not care that the engine has been in the same trim pin hole the entire time. You have made changes to the boat (I took the liberty of reading your identical post in Boathouse). With any change in weight and weight distribution the engine trim usually has to change. Not only that but the 3rd pin hole from the transom is pretty far back, specially for an engine that is not known for good bottom end horsepower and torque. You are the one asking for help and suggestions here. Answering that the trim pin has always been in the same location is a bit argumentative. There are some very knowledgeable folks in here that can help if you let them.


I have outlined that the only changes made were to the spark plugs fuel filter, lower unit oil. Also i have mentioned "The weight has not changed much only one extra person, my son who weighs 100 lbs".

I suppose ill trouble shoot on my own and post the fix.


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 Post subject: Cannot get on plane
PostPosted: 09 Aug 2016, 11:44 
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Joined: 17 Apr 2014, 15:39
Posts: 469
Location: Cullman, Alabama
Try the second pin hole like Pappy suggests and give it another try.

You also will want to check your compression and spark. It is possible something happened and your motor is not running at peak performance despite sounding like it is running fine. It would be great if you knew your previous compression numbers from when it was running well so you have a baseline to compare to.



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http://www.tinboats.net/forum/viewtopic.php?f=21&t=40764
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 Post subject: Cannot get on plane
PostPosted: 09 Aug 2016, 12:48 

Joined: 24 Mar 2010, 00:02
Posts: 434
thunder61golf wrote:
Pappy wrote:
Before you go pouring money into parts you are not sure you need why not tuck the motor in farther against the transom and run again.
Anytime you add weight you may need to trim in to get it on plane.
Also, not quite sure here. You indicated you have run @ 28mph at 5200 one time. Is it capable of that now with the same load you ran it at?
You also stated 20mph but no RPM. Was that at WOT? Same trim angle? More information we have the more accurate feedback you will receive.


The motor is a manual trim, and has been ran in the same location every time i have had it out, 3rd hole from the transom (6 total).
I believe it is capable of running 28 consistently. The issue is it has been running 18-20 MPH and wont go past that.
The weight has not changed much only one extra person, my son who weighs 100 lbs.


thunder61golf,

Pappy is trying to give you very good guidance. He is trying to systematically trouble shoot your issue over the internet. Believe me, that is a very hard thing to do because the poster is giving information and observations that the advice giver has to sort through. It is much easier to evaluate a motor in person. Pappy is a very well educated and seasoned Marine mechanic and engineer.

You made reference that your boat and motor was capable of running at 28 mph at 5200prms. Now you state that it will go a maximum of 18-20mph at WOT wide open throttle.

Pappy has inquired what are the RPM readings now with your motor at WOT and only going 18 to 20 mph. If your not reaching rpms of 5200 rpms, then your motor may have an electrical or fuel delivery issue or even a compression issues with one of your cylinders.

If your are reaching RPMs of about 5000 to 5200 and only going 18 to 20 mph, then you may have to tilt trim issue with the motor. If you have recently done a modification of your boat, then that extra weight can affect performance on the water. The tilt angle of the motor may need to be adjusted to compensate for extra weight.


Example.

I have an 14ft Modified V hull aluminum boat. I have a 1984 Evinrude 15hp motor on the back. With just me, the fuel tank and fishing stuff, I can go about 24 to 25mph on the water. If I bring my 190 lb brother fishing with me I will go about 18mph. I have to adjust the tilt angle of the motor to next spot on the motor clamp assembly to get the boat to travel at 22 mph. The extra weight and distribution affect performance. Smaller boats and lower horse power motor are affected greater with addition of weight and angle of trim of the motor. Larger boats with higher horsepower are not as easily effected by addition a little weight or another fisherman in the boat.

Cheers,

Cajuncook1


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 Post subject: Cannot get on plane
PostPosted: 09 Aug 2016, 12:57 
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Joined: 12 Dec 2014, 14:32
Posts: 1559
Location: New England
Boy oh boy :roll: , please don't ever be dismissive of Pappy's advice ... he's forgotten more about OBs than most of us will ever know. Any of us here - out in cyberspace - as only as good when helping YOU out with advice as dependent on the info that YOU yourself 1st give us!

Rant over ...

That said, I think you may have the wrong prop, so check it vs. the prop calculator posted in the Motors forum. If you need a hull, use a 16' Starcraft Fishmaster, as that is also a side-console model with a floor configuration.

FWIW I ran mine (exact hull referenced above) with a '96 vintage Merc 40hp that power trim/tilt and I could shoot it up onto plane no problems, where the WOT was 29mph. I estimated my hull weight was 700-800 pounds and between the battery, anchors, cooler and extra gear I ran the calculator with 195-pounds of extra gear carried and 2 aboard. The prop pitch (12") recommended by Turning Point was dead-nuts on ... I could turn screws within 100 RPMs of the rated max.

FYI - I have a small 12' tin with 8hp OB and "trim" of the weight carried in the boat - weight fore or aft - affects it greatly! You're complaining you only added your kid of 100-pounds ... well on my little skiff, I only added my little girl of 50-lbs soaking wet - and without moving the trim pin - I went from 18mph and easy to get up on plane to 12mph and struggling to get up onto plane. The further aft she sat, the better it planed out.

So check the hull when running for optimum trim pin position. And get this ... yes, you may need to move the pin dependent on the load carried and WHERE that load is carried (fore or aft). In fact, I'll be so bold as to suggest that you WILL need to move that pin depending on the # of people carried.

Personally if I were you, I'd invest in an after-market hydraulic trim/tilt bracket. I'd never use an OB of that HP with a fixed trim, that's just crazy ...



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#1) 1st tin rebuild, 18' Lund viewtopic.php?f=21&t=36583
#2) 25' Parker refurb from EMPTY hull http://www.classicparker.com/phpBB3/vie ... p?f=15&t=6
#3) 16' V-tin rebuild viewtopic.php?f=21&t=36465
#4 Procraft SV14
#5) 16' Starcraft entirely NEW Transom Skins viewtopic.php?f=3&t=37548
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