Can't get on a plane....what to do first

[Gas Giant]

I'm re-posting this one here, mainly because half the posts I got in other areas are basically telling me to get rid of my engine - not a lot of love for our engines out there! Since an engine swap is out of the question for me for the forseeable future, I thought I'd ask in here with other Force owners.

The boat is a 1988 17 foot Cobia center console. Originally it had a 75hp Suzuki, but now it has a 50 hp Force, late 80's era. Obviously a lot less power, and that may be part of the problem. The engine has great compression (135 on each cylinder), and is firing on both plugs. It fires right up and runs smooth at the first bump of the key. (largely due to members of this very forum! )

When I drove the boat for the first time on Thursday, it wouldn't plane out, and the boat was moving very slowly at full throttle. It was also making a huge wake for how slow it was going. I don't currently have a tach, but guessing by the sound it didn't sound anywhere near WOT. (I did verify after I shut the engine down that the linkage IS in fact opening the carb butterfly fully). I had myself and one other person in the boat with me; me sitting in the center and him sitting on the seat nearest the bow.

My engine doesn't have a power tilt setup, so I had to go to an island to adjust it since I have to get behind the engine and move a metal rod to a different hole. It was fully trimmed out on my way out - I adjusted it to a center hole, but it made no difference in how the boat drove on the return trip.

Also, my boat burned nearly all of my 6 gallons of gas for what is in reality a short trip - the island and the boat ramp are within sight of each other, albeit they are still a good distance apart.

So, I may have two problems - my prop pitch is 13 1/2 based on the part number. Not sure if this is a good prop for my boat.

The other is that my engine is mounted too low, but I can't set it up any higher without a jack plate. My anti-cavitation plate is 1.5-2" below the lowest point on my transom. See below:

I couldn't get a clear picture of what the symptoms of my engine being mounted too low are, so I don't know what to do first. I did get advice to check and see if I am carrying around a lot of extra water below decks, and I will do that as soon as I figure out how.

Any ideas? I'm still hoping I can use this boat with the current engine for the summer, and until I can afford an engine swap sometime next year most likely. I don't expect it to be a speed demon, but it feels like it really should be faster than it is (naturally, my speedometer on the boat doesn't appear to work....or I was going too slow to register....)

As always, thank you in advance, and I apologize for the lengthy post!

 

[puddle jumper]

Re: Can't get on a plane....what to do first

my 50HP force will do only about 25-27 mph on my 17 footer. Check your speed with a GPS. You can also manually trim your engine.

 

[Frank Acampora]

Re: Can't get on a plane....what to do first



Get rid of your engine---LOL

13 1/2 is WAY too much pitch. It will not let the engine rev up into its power range. Thus, the boat just digs a hole--even at full throttle--and can't climb out. So, you are at full throtttle and using as much cgas as the carb jet will pass. Drop down to 11 1/2 pitch and see what that does. You should be able to find a used one on ebay. Any pin drive 14 splined hub for Chrysler or Force will fit. 10 3/8 diameter X 11 1/2 pitch.

To raise the engine, you do not necessarily need a jackplate A couple of pieces of aluminum sandwiching the transom with equal thickness wood the height you need will do nicely. Search some posts on non repair engines. I think there are a couple of photos there.

Here's what I did to raise the transom on this little boat with aluminum and a fiberglass slug inside it. This boat top at 45 MPH and uses a 13 1/2 two blade prop on a 50 like yours.

 

[Robert D]

Re: Can't get on a plane....what to do first

Easy test for waterlogged foam under the floor: Park the trailer with the bow up. Plug out. Put a bucket under the drain and check the next morning. If it dripped all night, you'll know. Before I rebuilt by whole boat, I'd get a half gallon of water out overnight. I eventually pulled a few hundred pounds of sopping wet foam out from under the deck.

By the way, the dark stain below the drain in the photo is not rust. It's the color of water stains from decomposing wood inside usually.

I'm betting a combination of being too heavy with wet foam, a motor mounted too low, and the wrong pitch prop are all contributing.....

 

[Gas Giant]

Re: Can't get on a plane....what to do first

Thanks for the info guys. When I got the engine, the seller gave me a spare prop, but it appears to be a 12 pitch. I guess it wouldn't hurt to try it.

As far as the wood rotting out - it wouldn't surprise me - wonder if I should try to find a solid, engine-less hull somewhere and swap everything to it.....

 

[Gas Giant]

Re: Can't get on a plane....what to do first

I leaned the boat back and let it drain into a bucket. I got maybe half a soda can's worth of water.

 

[chosos]

Re: Can't get on a plane....what to do first

this almost perfectly describes a problem i'm having with my 87 force 50 on a 13' bayliner bass sriker.

we can hardly get ours on plane, and generally someone has to sit at the front of the boat. once its on plane, the thing runs like a champ. however, prior to that - we're doing the same thing you are - eating up fuel, churning up lots of cavitation, etc.

on mine, i've replaced the fuel pump diaphram, carb, points, etc - and it didnt help.

i believe my prop is also the 13 1/2.

 

[Bigprairie1]

Re: Can't get on a plane....what to do first

Easy test for waterlogged foam under the floor: Park the trailer with the bow up. Plug out. Put a bucket under the drain and check the next morning. If it dripped all night, you'll know. Before I rebuilt by whole boat, I'd get a half gallon of water out overnight. I eventually pulled a few hundred pounds of sopping wet foam out from under the deck.

By the way, the dark stain below the drain in the photo is not rust. It's the color of water stains from decomposing wood inside usually.

I'm betting a combination of being too heavy with wet foam, a motor mounted too low, and the wrong pitch prop are all contributing.....

Big Ditto on this!!. If you get a chance, take your boat over the local weigh scales and find out if you are trying to plane a 2500lb boat (assuming its supposed to be substantially less) with an incorrectly pitched 50hp engine.
Good luck tho'
BP

 

[Frank Acampora]

Re: Can't get on a plane....what to do first

CHOSOS: Your situation is a little different because your boat is smaller and probably propped correctly. The problem is weight distribution. On that little 10 foot boat in the photos above, I need to lean way over the steering wheel to get her to break over into plane. Before that she will only do about 10, digging a hole in the water. Once she breaks over, she picks up and darts away. But, that's the nature of small racing hulls.

In your case, first you need to experiment with the trim pin setting. While I generally don't think much of them, I think you ought to try a hydro-foil (whale-tail). It may just give you the extra lift at the stern that your boat needs to break over into plane.

 

[chosos]

Re: Can't get on a plane....what to do first

CHOSOS: Your situation is a little different because your boat is smaller and probably propped correctly. The problem is weight distribution. On that little 10 foot boat in the photos above, I need to lean way over the steering wheel to get her to break over into plane. Before that she will only do about 10, digging a hole in the water. Once she breaks over, she picks up and darts away. But, that's the nature of small racing hulls.

In your case, first you need to experiment with the trim pin setting. While I generally don't think much of them, I think you ought to try a hydro-foil (whale-tail). It may just give you the extra lift at the stern that your boat needs to break over into plane.

well, i ordered one of those hydro foils. OP, i'll let you know if it improves the situation for me at all. if so, maybe it will help you, too?

 

[sschefer]

Re: Can't get on a plane....what to do first

I'm re-posting this one here, mainly because half the posts I got in other
areas are basically telling me to get rid of my engine - not a lot of love for
our engines out there! Since an engine swap is out of the question for me for
the forseeable future, I thought I'd ask in here with other Force
owners.

Like Frank say's you have to get the bow up over the bow wake to acheive plane. While you could have everyone run forward (effectively raising the stern), the whale tale may work to do this for you but only if you first do your best to have the weight in the boat evenly distributed.

You don't have the option to replace your motor with one that is more fitting so you'll need to learn to make some compromises.

 

[Gas Giant]

Re: Can't get on a plane....what to do first

Got no problem with making compromises. Actually going to be getting a jackplate installed next weekend hopefully, and I'll try out my 12 pitch prop and see if any difference is made.

Other than that, I guess it means scrapping the hull and swapping all the good parts to a different, lighter one.

 

[mauiboy]

Re: Can't get on a plane....what to do first

Are your sure that you are getting enough spark. did you check to see if you are firing on both cly. I had a similler prob. on mine it would not get on plane after advices by this forum it turned out that my power pack was bad.

 

[Robert D]

Re: Can't get on a plane....what to do first

Deleted post....thought we were still on the 18ft Cobia...got confused

 

[Gas Giant]

Re: Can't get on a plane....what to do first

Robert - I think we still are! If you had any advice, post it! Unless it was to go boating with the plug out and pretend not to know anything about a 17 foot Cobia when I manage to swim back to shore....

Maui, good advice, but yeah I went through nearly the same thing before I even hit the water. Cyl #2 wasn't firing, turns out it was a broken wire. They're both sparkin now.

 

[Gas Giant]

Re: Can't get on a plane....what to do first

Speaking of which, does anyone near Cocoa, FL, know where to get a boat/trailer weighed?

 

[Robert D]

Re: Can't get on a plane....what to do first

I leaned the boat back and let it drain into a bucket. I got maybe half a soda can's worth of water.

What's important here is if the water drained out immediately then completely stopped.....which could be rainwater or whatever; Or if the soda can's worth of water drained out over night. If it drained out over night, that means something is holding water inside the hull and is slow to release it. We're talking about either saturated foam, rotton wood in stringers or decking, or the transom. First place to look.....I would remove the drain plug insert, i.e. The casing the drain plug goes into. It was probably just drilled into the transom, slapped into the hole and 3 screws put it with no sealer. Take it out and inspect the wood inside the transom. That will tell you a lot. #1 place to find rot there. (If it's okay, get the marine sealer from 3M at Home Depot....good stuff.....and install it correctly.) I can say that an 18 foot tri-hull with several hundred lbs of saturated foam, rotted stringers and transom leaked overnight about a half gallon of water. The amount slowly subsided over a month. Tore into it, and you'd never guess any water had drained out.....you could squeeze a handfull of foam that was 70%water! Over the year or so I rebuilt the boat, I left a piece of foam about 8 inches square in the corner of the garage floor, periodically seeing how long it took to dry in the open air. After a year, it was dry in about 2 inches of the top. The rest never gave up the water. This was the old style foam....not the 'closed cell' stuff that is newer.

 

[Robert D]

Re: Can't get on a plane....what to do first

Speaking of which, does anyone near Cocoa, FL, know where to get a boat/trailer weighed?

Any truck weigh station you see on the highway....it's free. Those are public scales. If you want to pay $8-$10 for a certified weight, you can also head to a truck stop and use their scale.

 

[Gas Giant]

Re: Can't get on a plane....what to do first

Robert - the water drained out almost immediately. I cranked the wheel at the front of the trailer as high as it would go and then walked to the back of the boat and looked - water was draining out.

to get it a little higher, I went and grabbed a small section of wood I had and stuck that under the trailer wheel (pulling a muscle in my back in the process - I keep forgetting I'm not 19 anymore). Went to check it again, and the water had stopped and I had the half a soda can's worth of water in the bucket. It had been draining for maybe 5 minutes at the most.

The next morning, the amount of water in the bucket hadn't changed. Unfortunately, it rained a lot yesterday, so that filled the bucket with rainwater...any measurements now are going to be waaaaaaay off.

 

[Robert D]

Re: Can't get on a plane....what to do first

A waterlogged boat will usually drip all night....that's good news if it completely stopped. You're going to have to get a prop on there that will get the rpms up, and see about getting the cavitation plate nearer the bottom of the hull. If that doesn't do it, time to take some core samples of the foam under the deck.....but I'd get the above stuff done first before you bother.