how to rise the bow

alone

Seaman Apprentice
Joined
Nov 15, 2002
Messages
39
Hi,<br />17' open fiber boat, 617 lb. weight-without motor-<br />25 hp new mariner marathon, 10,38 dia.* 11 pitch three blade prop. I tried all five trim positions<br />but I couldn't rise the bow at planing. Is the power of the motor not enough for it or are there any other necessities to change ex: pitch...<br />Thank you very much...
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: how to rise the bow

Put a string or straightedge on the running surface of the hull from the transom to about 4' forward and tell us what you see.<br /><br />Good luck!
 

Forktail

Ensign
Joined
Feb 11, 2002
Messages
977
Re: how to rise the bow

That boat/motor combination seems underpowered to me. Whats the boat rated for?
 

ob

Admiral
Joined
Aug 16, 2002
Messages
6,992
Re: how to rise the bow

I agree, a 25hp is not going to lift a 17ft figerglass hull much, regardless of trim position.Heaven forbid its got a hook in the hull.
 

digimortal777

Petty Officer 1st Class
Joined
Jun 25, 2002
Messages
214
Re: how to rise the bow

" posted December 29, 2002 01:25 PM <br />--------------------------------------------------------------------------------<br />Hi,<br />17' open fiber boat, 617 lb. weight-without motor-<br />25 hp new mariner marathon, 10,38 dia.* 11 pitch three blade prop. I tried all five trim positions<br />but I couldn't rise the bow at planing. Is the power of the motor not enough for it or are there any other necessities to change ex: pitch...<br />Thank you very much..."<br /><br />you say you want to raise the bow AT planing......no you dont....your boat shouldnt have a bow raised if you are on a plane
 

alone

Seaman Apprentice
Joined
Nov 15, 2002
Messages
39
Re: how to rise the bow

digi, I know it will not rise too much at planning but mine is diving...
 

Mumblerone

Petty Officer 1st Class
Joined
May 12, 2002
Messages
344
Re: how to rise the bow

Move a lot of weight to the back. You're pi**ing up a drain pipe. See what happens. :(
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: how to rise the bow

If your boat is running with the bow too low<br /> there is something wrong with your boat or the set up.Have you checked for a hook as we suggested in the other posts.<br /> The motor is a little small but a boat with<br />tiller steering should run without the bow so low.<br /> By the way with tiller steering you should be steering with your left hand and sitting on the starboard side.
 

radsrh

Petty Officer 1st Class
Joined
Oct 30, 2002
Messages
250
Re: how to rise the bow

If your bow is diving are you even planing, a 25 on the back of a 17' seems way underpowered to me.
 

alone

Seaman Apprentice
Joined
Nov 15, 2002
Messages
39
Re: how to rise the bow

Spike, <br />I tried to control every situation as you told before. I checked the hull but didn't see a hook or any other wrong.I am sitting on the starboard side; gas tank too. Lying to left problem continuing at planning a little bit. I am tring to rise bow so I hope to eliminate left lying.
 

Forktail

Ensign
Joined
Feb 11, 2002
Messages
977
Re: how to rise the bow

If your boat is getting up on step and planing ok, but not trimming the bow up once on plane, you may not be getting enough trim angle out of your outboard/transom design combination.<br /><br />Not sure what boat you have, but most boat hulls have a 10-15 degree transom angle, with 12 degrees being common. If your angle is greater than 12 degrees, you may need to shim the transom/outboard combo with a tapered plate or something.<br /><br />It would be interesting to know what your transom angle is. You can measure your transom angle using a little trig.....<br /><br />Measure the distance along the boat's transom from the point where the outboard rests on the transom to the bottom of the keel (lowest point on boat bottom). Next, make sure the boat is level and tie a weighted object on a string and hang it from the same point on the transom where the outboard rests. The weight should hang down toward the ground, but not touch. You can use tape to hold the string. Next, place a straight edge along the bottom of the hull keel. Make a mark on the string where the straight edge touches the string. Then measure the length of the string from where the outboard rests to the mark on the string from the straight edge. Try to be exact, say to 1/10 of an inch.<br /><br />The measurement along the transom/hull will be your hypotenuse length. The measurement along the string will be your adjacent length.<br /><br />Since cosine = adjacent/hypotenuse, you can easily find the "X" angle by taking the inverse cosine of the adjacent angle divided by the hypotenuse.<br /><br />For example, lets say the measurement along the transom hull is 20.8" and the measurement along the string is 19.9"....<br /><br />cosine of X angle = 19.9/20.8<br /><br />so, X angle = inverse cosine of .9567307<br /><br />X angle = 16.92 degrees.....maybe more than your Mariner's trim adjustments can handle (for example).
 

Reel Appeal

Chief Petty Officer
Joined
Aug 19, 2002
Messages
566
Re: how to rise the bow

alone,<br /> With the boat/motor out of the water.Put the motor in the down position.Check to see if the cavitation plate on the motor is in line with the bottom of the boat.If you are using a motor with too long a shaft it will create drag and hamper your ability to plane.Long shaft or short shaft? ;)
 

Hooty

Rear Admiral
Joined
Oct 2, 2001
Messages
4,496
Re: how to rise the bow

We had a long discussion about this boat and engine about a week ago. Alone sez it's a long shaft (25" I guess)engine but I don't think he ever said if the boat had a long or short shaft transom. Which is it?<br /><br />c/6<br /><br />Hooty
 

rons boat

Petty Officer 1st Class
Joined
Dec 28, 2002
Messages
210
Re: how to rise the bow

Try a gps to note speed and repeat trim settings to determine if you have range of adjustment to get max speed with hp available. If not in the range of adjustment, out of the envelope, your max speed will be at one end or the other of adjustment of trim. Lets assume you have achieved proper trim but still can't get it up. A tach or sharp ears would tell you if your motor is developing its maximum output(reaching rated rpm) on your boat. With a low enough pitch even the smallest motor could still develop its rated horsepower and not lift the boat on plane. In short a higher hp motor might be required. Experience tells me you are probably on the low side of required engine size. Important: What does the data plate on your boat give for max hp? A good guide is no less than 1/2 the max is the min.
 

alone

Seaman Apprentice
Joined
Nov 15, 2002
Messages
39
Re: how to rise the bow

Transom angle is 13 degrees, at the third position of trim ( from bottom) the motor shows 90 degrees.<br /> Transom height is 20''<br /> Motor shaft is long, 20''<br /> Manufacturer says 9,9 - 30 hp motor is ok.
 

Mumblerone

Petty Officer 1st Class
Joined
May 12, 2002
Messages
344
Re: how to rise the bow

Who's the manufacturer and can you send PICs? Are you getting up to full RPMS? :( ;)
 

roscoe

Supreme Mariner
Joined
Oct 30, 2002
Messages
21,753
Re: how to rise the bow

Please tell us a little more about the boat and motor.<br /><br />Who is the boat manufacturer?<br />Do they have a web site?<br />What shape is the boat hull? <br /> V-hull, modified v-hull, Tri-hull?<br /><br />And the motor, how does it run? <br />Does it idle properly? <br />Does it accellerate properly? <br />Does it run smoothly? <br />Does it achieve high rpm's at full throttle?
 

roscoe

Supreme Mariner
Joined
Oct 30, 2002
Messages
21,753
Re: how to rise the bow

You stated the bow is diving. <br /><br />Does it rise up, then dive, then rise up, and then dive again?<br /><br />Does the bow ever rise up??
 

alone

Seaman Apprentice
Joined
Nov 15, 2002
Messages
39
Re: how to rise the bow

Boat manufacturer is in Istanbul / Turkey.<br />look at www.taylanyat.com and try to open STAR 520<br />model. My boat is the open version (cabinless)of <br />it, made by another manufacturer. <br />Engine is new and very healthy.
 

alone

Seaman Apprentice
Joined
Nov 15, 2002
Messages
39
Re: how to rise the bow

roscoe<br /> the planing stages normal but bow is too low at planing.
 
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