Yes another motor height Question

1990 Bayliner 1700 Capri, 1990 50hp Force 507x90D,
I`ve had this boat for 2 seasons now and it runs decent with 2 adults and 12 gals. of fuel on board. I`ve always thought that it takes its time getting on plane but not bad. Recently we have been having a 3rd person along and this when it really takes its time coming on plane. I looked at smart tabs and with the way this hull is shaped in the back they would be a difficult install.

Well with all of the threads on motor heights it suddenly clicked in my head to check this one out.


Bottom of the vent. plate to the hull is 2.5 "
So I need to go up with the motor a couple of inches and there isnt enough transom left to do that. Not only that but in looking at these pics this morning to write this. Is it just me or does that motor look like its leaning to the port side? it would explain why it always wants to pull to port all the time, gotta hold on to the wheel all the time.



I guess I didnt get a good shot of the bolt holes but there isnt room to go up on the motor. I`m thinking jack plate. I`ll go out in awhile after this rain stops and get another pic.

Re: Yes another motor height Question

That engine was never really a powerhouse. Raising it will help some but don't expect miracles--if lucky, you might gain 1-2 MPH.

If you have a tachometer check that RPM is up near the top of the rated at wide open throttle. It should be running around 5000-5500.

Small boats and engines are more sensitive to loads than larger ones. Therefore: If the engine is below its rated RPMor even at its rated rpm, with a third person try a prop 1 or 2 pitches lower. That is, if you now have a 10 3/8 X 13 try a 10 3/8 X 11 or 12. Also check the position of the tilt pin. If it is set too far in towards the transom the boat will steer heavy and the bow will plow. Experiment with hole position.

The engine does appear skewed BUT look at the right wheel of the trailer--it appears tilted too. That may just be an optical illusion of the photo.

Search some posts of our departed Tashasdaddy. He had excellent photos of a really simple plate to raise the transom.

Change one thing at a time and you will make some progress in small increments.

Re: Yes another motor height Question

Frank, I dont have a tach so not sure on rpm. I have experimented with pin position, with 2 people I can run 3rd hole from transom and with 3 I have to drop to 2nd.
The only #s on the prop are 11 1/2 on one side and A12 1 on the other.
I will run a search and check the posts of Tashasdaddy. Thanks

Re: Yes another motor height Question

Like Frank said you don't have a lot of hp and you do have a very complicated hull; one that isn't flat which plane out the easiest. The more V the harder it is, but you do have nice lifting strakes which surely help. However, the more complicated the hull the more it usually weighs, laying glass and stringers in all the nooks and crannies. Your bait boxes hanging off the transom don't help either.

Drag from too much engine in the water definitely has an effect on performance, BTDT, but again as he said who knows how much you will gain. Personally I would get it up as mentioned and go from there and again as he said, I wouldn't expect miracles.

HTH,
Mark

Re: Yes another motor height Question

I'd do several things to make the boat/engine combo more practical for the way it's used in the real world:

>Get the AV plate up 2" above the bottom (at least)

>Get tabs.

>Get that thing a 4-blade prop of a certain pitch size so that when it's lightly loaded (one person, half tank of fuel), you can make test runs up to, or slightly above, the MAX RPM range. (When loaded up, the engine will fall into the middle of the acceptable max RPM range). At light loads, you want to be 'underpropped' and self limit RPMs.

Re: Yes another motor height Question

Ive been doing some searching and found Tashasdaddy`s transom plates. He made his out of 3/16 alum plate and 3 pcs. of ply, but I need to hang a 50hp on this thing. I found these online and they are made from 3/8 alum, Whatcha think guys?
http://www.boatersland.com/thmjp4fadp.html

Re: Yes another motor height Question

Im going to send some pics to Nauticus and see what they have to say about tabs. Port side will be okay I think but my ladder is on the starboard side, may have to lose the ladder or come up with another idea. I`m going to order a tach today also so I know whats going on there.

Re: Yes another motor height Question

If the boat doesn't purpoise I wouldn't bother with the trim tabs.
I would raise the motor up at least 3"
and did you ever consider hydrofoil fins on your motor?
They will help get you up on plain and once you're there they are out of the water so to not slow you down.

Re: Yes another motor height Question

I certainly agree with less engine in the water means less drag, but a lot depends upon what you are doing, with what, and in what kind of circumstance.

If you are a race guy then a chopper prop running with just the lower half of it in the water at 10k rpm's and 90 mph is ok fine. But if you are out fishing and it gets a little rough if you are too high, you will ventilate every time a wave comes by and you will burn up a lot of fuel and not get very far. You have to adjust to the conditions and live with it.

Edit. Forgot about the Bassboats. A lot of the 65 mph rigs have a bottom that stops roughly a foot short of the transom. Then they have the engine on a variable height jack plate that is another foot or two aft of the termination of the bottom which allows them to move the engine up and down under certain circumstances along with moving the trim around. Surely, on a rig like this, if you put a strait-edge down centerline of the bottom, the anti-vent plate will be several inches above the line when they are doing their 65 mph.....but back there the prop will be well submerged and getting maximum thrust. The farther back you mount it the higher you mount it due to the way the wake comes out from under the hull for top performance.

Course as I said, when these whopee boats get into Lake Erie waves, the speed drops, the jack plate goes to the lowest position and they make their way back home best and dryest they can.

Mark

Re: Yes another motor height Question

This will fix you right up.

http://www.thmarine.com/products/Ou...C-Static-Jack-Plate-5-inch-vertical-extension