Boat won't plane out

Olias · Jun 8, 2013

I have a 12' Starcraft Alum. boat that I just recently started using a 96' Mercury 8hp motor with. The motor is more than enough power for what I use it for but at 1/2 to full throttle the nose of the boat sticks WAY up in the air. Looks silly. I have tried re-arranging things a bit putting the 6 gal. fuel tank more towards the middle of the boat etc., but it still will not plane out worth a beans. I was/am considering buying this motor but if I can't get this figured out it's a no go. I'm aware of the 3 different tilt angles it has but adjusting to any of them only makes it worse. It's almost like it needs to tilt in more (towards the transom) to kick the nose down, but of course it can't angle forward any more. Currently it's straight up and down flush with the transom. Is it possible it needs a different type of prop? I've heard there a different styles like for speed, power, etc. Any thoughts? Thanks

metriccrescentwrench · Jun 8, 2013

Re: Boat won't plane out

It sounds like the engine needs to tuck in more. There's something called a wedge plate that might help, they go between the engine and transom to allow for more negative tilt. I've never used one so can't offer suggestions on brands etc., but if you search online I'll bet you can come up with one.

blackhawk180 · Jun 8, 2013

Re: Boat won't plane out

You are correct expecting the 8hp to plane you and have already taken the first logical steps of moving weight forward. It really sounds like the motor needs to be trimmed in more (as you also noted). I have a merc 8hp and quite familiar with the operations. Can you post a pic from the side showing the angle of the transom and motor when trimmed in as far as possible? That would help a ton.
Also a pic of the boat from the stern so we can see the height of the motor and what kind of planing hull you have. Prop pitch is down the list but not out of the question at this point.

Don Hansen · Jun 8, 2013

Re: Boat won't plane out

You didn't say if it will plane at full throttle. If it will get up it on plane then back off.

I use to get a 12 ft flat bottom up on plane with a 5-1/2 hp but I had to sit on the middle seat. Temporarily tape a stick to the tiller to see if it works.

You have to remember that with 2 light boats of the same type, one 12 ft and one 14 ft, the 14 will plane easier. Just like an airplane with a bigger wing.

DLH

steelespike · Jun 8, 2013

Re: Boat won't plane out

Is it basically you the motor and the gas tank?What do you weigh? What size prop? probably near the base of the blades or under the prop nut. The 8 should be able to make close to 17 or 18 mph on a light boat.

Sea Rider · Jun 8, 2013

Re: Boat won't plane out

What's the max engine stated for that boat ? Will need a minimum of 70% of it's stated HP to perform as nearly expected. Trim engine to be perpendicular to water level, move yourself towards middle deck, full wot to plane. If not, that engine is lacking trust to bypass resting inertia, hull drag against water, have nose down and plane the boat.

To assume the combo will plane with different prop is a wild guess, will need a big suitcase full of props to try them out, including hooking an induction tach and under trial and error check which gives best hole shot and good overall performance. Better go for a bigger 9.8, 9.9, 15, 18 HP engine, will perform much better.

Happy Boating

nimmor · Jun 8, 2013

Re: Boat won't plane out

I had a similar problem with a small boat I used to have. I just didn't have enough weight in the front. I used the trolling motor on the bow so I moved the battery for it up front and it worked. This also made my battery more efficent because the wires were shorter. I know people who just put a sand bag in the front to add weight.

tomhath · Jun 9, 2013

Re: Boat won't plane out

steelespike said:
Is it basically you the motor and the gas tank?What do you weigh? What size prop? probably near the base of the blades or under the prop nut. The 8 should be able to make close to 17 or 18 mph on a light boat.

I suspect steelespike is onto it. If you weight 165 lbs and have a small gas tank you might have motor trim issues. If you weigh closer to 300 lbs you probably would be happier with a bigger boat.

Olias · Jun 9, 2013

Re: Boat won't plane out

Thank you one and all for the responses and great questions. Sorry I didn't get back sooner as a small family crisis had me away from the computer all day. Anyway....I will take and post pics today (when I get back from fishing

) as requested. I will check the specs for max HP etc. for this boat. Duh, never thought to check that. FWIW I'm a skinny little dooger. I'm 5'9" and weigh 145lbs. My son who weighs about 180lbs. is always with me and riding in the nose. I'm currently only using a 3 gal. plastic tank which is (for now) in the rear of the boat. I gave up bringing my elec. trolling motor and 2 batteries as that just made it ridiculous. So basically just motor, tank, me in the rear and my son up in the nose. Not counting a few tackle boxes, rods, and lunch box that weighs nothing. I will report back with more info.!

-B-

Olias · Jun 9, 2013

Re: Boat won't plane out

FWIW I just ran out and took a look at the BIA Specs on the transom. They are as follows....10HP, 3 people, and 600lbs. max weight with people, motor, and gear. I'm definitely not exceeding those numbers. Does the 10HP spec mean that's what they recommend or that's the max hp for this size boat and hull type? It doesn't say max, just 10hp. I suspect that is what they recommend. Hopefully I'll be able to determine that later this summer as I am currently rehabing a 1960 Evinrude Sportwin 10hp that I just got from a guy. Anyway, that's the info. I have for now. If I get a chance I might even be able to post a pic before I leave for fishing.

-B-

Olias · Jun 9, 2013

Re: Boat won't plane out

Update....ok, ran out to take some quick pics for you guys. Hope I took pics of what you need to see. If not let me know. On closer review I see that the info. in the BIA Specs tag says "up to" 10 hp, so I should be okay with an 8hp but a 10hp would probably be better. The other thing I noticed is that to me the motor seems to be almost tilted in a little towards the transom more than I originally thought (the way I feel it needs to go in more). So that's kind of weird. My lack of knowledge at this point would think that's enough of an angle to plane out. Shows ya what I know.

The other pic was an attempt to show the front of the boat so you had an idea of the hull style. Is that what you were asking for? The other pic is just trying to show the basic lay out of gas tank etc. Let me know if these pics help. Thanks.

-B-

pootnic · Jun 9, 2013

Re: Boat won't plane out

I think someone already asked you,if you ever tried opening it right up.
Sometimes you just have to get over the "hump",then it will plane out,maybe porpoise.
Other than that,move more weight up front...that hp should be work fine.
Small light boats,are very weight sensitive.

Olias · Jun 10, 2013

Re: Boat won't plane out

Sorry I didn't answer the wide open throttle question. Yes. That's when it's the worse. There is no getting over the hump at any speed. I think you are all correct in that it's just a small light boat and very sensitive to loads. I went out fishing again yesterday and have learned that 1/2 throttle or less gets me to where I need to go quick enough on the relatively small lake I fish the most and the non planing attitude of the bow isn't so bad that I can't live with it. Thanks for everyone's input. Very much appreciated.

-B-

metriccrescentwrench · Jun 10, 2013

Re: Boat won't plane out

Well, after seeing your photos I don't think the engine needs to be tilted in more. In fact it looks to be tilted in more than need be. That little boat with an 8 HP engine ought to be able to plane easily. When I was a kid we had a smallish aluminum boat rated for 25 HP with only an old Johnson 7.5 HP on it, that boat would plane with no problem with me driving plus two adults. It was definitely much slower than with just me in it, but it would certainly plane (the point is that it doesn't sound like you're underpowered).

Is it possible that you have an engine problem and it's not putting out full power? Have you checked to make sure you have spark on both cylinders? Checked compression? What do the spark plugs look like? Another possibility might be a spun prop hub (heck, I don't even know if that's a possibility on an engine that small, but if it is you can check it by putting a mark on the hub and prop and seeing if the marks move in relation to each other after using the engine).

hotshott · Jun 10, 2013

Re: Boat won't plane out

Olias, From the looks of the pics, I see what is known as a deepV hull 14 foot boat. Strakes are outward as they should be. And I say this cause I own a Bayliner 185BR with inward strakes which makes it more economical to operate, Plane up faster and overall better performance. Motor appears to be tilted proper but at 8 HP your pushing a lot of boat up and out of the water with only 8 HP. Yes you can move some gear around but a second passenger will take care of the weight problem as well. My experience with small boats is more HP. I would look for a 15HP, but that's me. The prop issue is a fine point as well. However the cost to buy a different prop and do the legwork to find the right one, That issue can be corrected as well with more HP... Good luck.

Sea Rider · Jun 10, 2013

Re: Boat won't plane out

Try trimming 1 hole out for engine to be perpendicular to water level once boat is floating, move son up front, go wot. If engine doesn't produce water splashes over, out transom, prop aireation, cavitation issues, you should plane fine. If not, try same test with you alone, if engine doesn't plane your are definitely under powered. Will need to live with displacement speed if it's ok for your particular boating needs. That 8 engine is on the minimum limit performance, definitely a 10 HP will be much better.

Happy Boating

metriccrescentwrench · Jun 10, 2013

Re: Boat won't plane out

I would look for a 15HP, but that's me.

The boat being discussed is rated for a maximum of 10 HP.

Try trimming 1 hole out for engine to be perpendicular to water level once boat is floating

Olias has already tried all the different tilt settings available, per the original post.

Olias · Jun 11, 2013

Re: Boat won't plane out

Thanks for pointing those things out metriccrecsentwrench because I was going to mention that I was getting confused when the BIA tag said 10hp max and folks are saying get a 15hp etc. Yes, I think a 10hp motor would be better but I have used a friends 12' alum. boat with either a 6hp or 7.5hp (can't remember which) and it planed out fine. I would however like to look into some of the other things mentioned a bit more as I am brand spankin' new to outboards. For instance the "spun hub" scenario you mentioned. I'm not exactly sure where to make these marks (what is considered the hub?) but I can look into it. As far as the spark plugs go....no, I have not pulled them and checked em' yet. At least that's one thing I CAN do and will.

But as far as both plugs not sparking...really? Can a 2 cycle motor even fire up let alone run on one spark/cylinder? I'm not being a smart alec here, I seriously don't know. I can only relate to car engines. I'd think if only one cylinder was firing that the timing would be so off that it would sputter, cough, shake, or what ever and have like next to no power at all. Yes/No? I will definitely check the plugs after work today and even get new ones to be safe. I'll also try to get someone to help me check the compression.Thanks again for all the input guys.

-B-

steelespike · Jun 11, 2013

Re: Boat won't plane out

Yes a 2 cylinder 2 stroke can run on one cylinder and the inexperienced operator not realize but for the lack of power.
Pull one plug wire at a time and see if it runs.
Also you could take everything out of the boat and do a test run with just you the motor and the gas.
It should approach 15 to 18 mph.
A 5 hp max is about 12 mph a 10 hp about 21.

Sea Rider · Jun 11, 2013

Re: Boat won't plane out

If plug test is ok, both cylinders working properly. Try to borrow a used in good condition same diam/pitch prop and test. So to be sure 100% this is your issue. Buy a new one and boat happily.

Happy Boating

Boat won't plane out

Petty Officer 3rd Class

Commander

Petty Officer 1st Class

Petty Officer 1st Class

Supreme Mariner

Supreme Mariner

Petty Officer 1st Class

Master Chief Petty Officer

Petty Officer 3rd Class

Petty Officer 3rd Class

Petty Officer 3rd Class

Attachments

Chief Petty Officer

Petty Officer 3rd Class

Commander

Cadet

Supreme Mariner

Commander

Petty Officer 3rd Class

Supreme Mariner

Supreme Mariner