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Old 30 June 2013, 21:28   #1
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3m bombard wont plane?

Ok got a question for you experienced fellas here.. little about my rib. its a bombard ax500 3m with a pvc hull and tohatsu 9.8 4stroke.

i normally take it out by my self or with the family. i weigh 180lbs and the family combined weights 160lbs. normally have a small cooler full and my tackle bag, i would guess somewhere in the 60lb range.. i normally have no problems planing and gps tracked at 20mph in that configuration.

today i took a friend out who weighs 205lbs, same cooler and tackle bag. i could not get this thing to get out of its own way, according to the gps at full throttle it was at a whoping 6mph.. so my biggest question are these boats really weight sensitive to 50 more pounds? or do i need to look for a problem somewhere else? Any help or ideas would be great. motor seemed to run pretty good, it hasnt been run in about a month but started first pull.
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Old 01 July 2013, 02:11   #2
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"You're gonna' need a bigger boat..." - sorry.



No, it's all about distribution - 205 lbs is a heck of a big lump to have sat in one place on a little rubber boat with a small engine. You will need to move him about to see if it will plane - these small 3 - 3.5m boats with low power engines are very sensitive to weight distribution when getting on the plane, normally shove/lean all the weight up front, accelerate to the plane and then move back.
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Old 01 July 2013, 04:16   #3
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I had the similar Zodiac version of your boat, with a 9.9hp 2 stroke Yamaha. It was before GPS so dont have exact figures.

It did plane with 2 big guys on board.around 420lbs total. The engine was obviously lighter than yours and had different power curve. Its possible you are right on the limit for getting your boat to plane, small boats like this are a bit all or nothing i.e. Flying along a 20mph on the plane or stuck punching the bow wave a 6mph instead. The difference can be just a few pounds or a couple of hp.

Try moving weight around as suggested above, or you could try fitting trim tabs or a doel fin.
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Old 01 July 2013, 05:32   #4
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The weight is the issue. But the amount of it may not be that critical. Where it is may count for more.It's not only your chum in question either. Get the bow up then get him forward to bring the bow down. You will then have to move forward until the balance is reached, at this point you then wait for the boat to gather speed and hopefully pop onto the plane. At this point you will have to adjust your weight to the stern to avoid the bows digging in.
It's an organic process when you don't have brute force. Make sure ALL tubes are up to pressure. Especially once in the water. You may need to adjust trim out a touch.
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Old 01 July 2013, 05:43   #5
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An interesting article, from your neck of the woods

http://media.channelblade.com/boat_g...tipstricks.pdf
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Old 01 July 2013, 05:50   #6
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Weight is the problem, try moving your mate...... to the car park
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Old 01 July 2013, 08:38   #7
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A longer boat planes easier than a shorter craft. You have 425 lbs plus the motor, gasoline, and boat weight you are trying to plane with a short hull. Even moving the weight around may not get it on plane.

Once you reach the limit of power the motor develops, expect to attain hull speed only. It is just physics. Possibly a prop with lower pitch would help, as you are probably not allowing the motor to reach proper RPM. You lose HP pretty fast when operating below rated RPM.

As far as the extra 50 lbs goes, a straw will really break the camels back you know.

Our 9.8 planes our 14 ft boat fine with my wife in it, but when my fishing buddy comes with me instead of my wife, it bogs the boat down below planing speed.
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Old 01 July 2013, 09:22   #8
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i figured weight was the problem. while we were out we tried to move the weight around a bit and it didnt change. the tubes were properly inflated as well. i figured i would ask here before i did anything. the way the motor sounded yesterday we were definitely heavy.

i have a buddy who has a 11ft baltic sib with the same motor and he runs great with 2 big guys, cooler, fishing gear and dive gear, ive gps next to him a wot and he was at 18mph. so im not 100% convinced the motor wasnt making the power it should have been. I have a tohatsu dealer near by so im going to see if they can set me up with a recommended prop for my application
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Old 01 July 2013, 09:44   #9
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Your friend has an 11 ft boat, so it would plane easier. Do you have a tach? Guessing at props can be the expensive way to go, but the Tiny Tach is not too expensive and would allow you to see where you are on the power curve with the boat loaded.

Also, he has a SIB with a different bottom configuration.
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Old 01 July 2013, 10:14   #10
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i dont have a tach but from the sound of the motor it was run about 1/2 the rpms it is supposed to run at. i realize he has a larger boat and way different hull configuration. i think the first thing i need to do is get him in the boat with nothing else in it. it should plane no problem. then start adding more stuff to find out what can be left behind. being able to plane is crucial where i fish. unfortunately he is the only person who is down to fish reliably, so figuring this out is high on the priority list. also its not difficult to find a 200+ person around here so if the prop guy is around that size finding the right prop should be a breeze.
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Old 01 July 2013, 10:47   #11
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Quote:
Originally Posted by ceejkay View Post
... also its not difficult to find a 200+ person around here...


They're becoming pretty common over here too...
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Old 01 July 2013, 12:38   #12
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The height of your outboard and angle of it will also have an effect on the ability to plane, try some minor adjustments to see what difference it makes
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Old 01 July 2013, 13:14   #13
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The height of your outboard and angle of it will also have an effect on the ability to plane, try some minor adjustments to see what difference it makes
that is one of the things i plan on doing. i need to take it out before hand to make sure everything still feels and acts right with just me.

i just talked to him a little bit ago. were gonna go out empty. get him placed to where it planes and then start adding our gear. without gear we should be right around my normal weight. i have a fish bag that i always bring for the fish that dont fit in the cooler, so getting rid of the cooler will save a ton of weight. i love my transom tank but i think that it might have to go for when i bring him. so i have at least a half day of figuring out what works.
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Old 01 July 2013, 13:50   #14
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I don't know how long your arms are but a short tiller extension will help you reposition your own weight forward.
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Old 01 July 2013, 14:28   #15
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I'm going to open up the worm can & ask have you tried a fin on the cavitation plate ? I've had lot's of success with them on every boat I've had when it comes to getting on the plane really quickly !!
Marmite product but £20 and four holes (easily filled) and if you don't like it stick it on ebay or the back of the shed.....
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Old 01 July 2013, 15:17   #16
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I'm going to open up the worm can & ask have you tried a fin on the cavitation plate ?
i have thought about it. when its just me, by myself in 1-2ft chop i get cavitation at higher speeds. so ive thought about it. but i wasnt cavitating. might be another option as well..
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Old 01 July 2013, 19:34   #17
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If that sib is rated for max 15 HP engine, a 9.8 is too poor to overcome hull drag and plane nicely if with more than 2 mates. Inflate sib to its factory recommende working psi pressure, move mates up front, go full throttle. If nothing happens, need a larger sib or more punchy engine.

Happy Boating
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Old 01 July 2013, 20:15   #18
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well mine isnt a sib. it has a hard pvc single core hull. and its rated for max 10hp
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Old 02 July 2013, 02:14   #19
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And some guys can be a bit like some women .. who never admit or believe their true weight
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Old 03 July 2013, 13:13   #20
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has anyone ever used the trim tabs? in theory they should work, but do they actually work?
Lifters trim tabs for inflatables
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