TOPIC: Scary handling

Hey guys,

I am new to these forums and it seems like there is a lot of good knowledge here. I am having a problem with my 1960 Silverline PT-140. It is 14 foot long, has a short transom on it, and a fairly flat bottom. Right now it has a 70 Johnson short shaft motor on it. The problem is that at high speed she pulls hard to the right. So I steer left to compensate and the right(I don't know all the port/starboard stuff) side of the boat comes way up out of the water. Incidentally, it is left hand drive with the old cable and pulley steering. With extra weight in the back, the problem is greatly improved. Some things I am considering are to put on a single cable steering system, maybe playing with the prop to reduce the top end speed, and maybe adding some weight to the right side. Does these ideas sound plausable, or it it just way too much motor. Any ideas would be greatly appreciated.

Thanks,

Joe

fairly flat bottom

get a long straight edge and check the bottom of your hull for a hook, a hook is a depression in the hull (low spot) that as the water hits the back edge of the depression it acts like a trim tab and will push the hulls bow down, on that side of the hook, or both sides if the hook is present on both sides of the hull


putting weight in the back or to one side is causing the CG to change and helping to avoid the hook

my 2 cents

Michael is probably right about the hook. You can't see them without a perfectly flat reference point, like a good long straight edge. Hooks often result from the way a boat sits on a trailer, i.e., the rollers or bunks end just before the end of the hull, and over time induce a hook.

70 hp isn't too much for that boat. I run 100 on my 14' Power Cat, and keep thinking I want more.

Do you have a trim tab on that motor to adjust for the pull you're getting? I'm not at all familiar with Johnson motors, but most outboards have some sort of adjustment for that torque created by the prop just spinning in one direction.

Your prop should be sized so that at WOT you are at some given max rpm. Again, I don't know much about Johnsons, and don't know what to tell you that would be. Props are science, then art!

You can get a new Teleflex system to replace the pulley system for a very reasonable cost, maybe a bit over 100 bucks. That would be a great improvement over the pulley system!

Good luck.

Frank

Hey Joe
Welcome aboard ..A couple of simple things you can check .Where is your motor trim set at ? If its angled way to close to the transom on some boats it will push the bow or the nose of the boat down and that can make it pull very hard to one side or the other . Second thing you can check is the little fin just above your prop . you can compensate for steering torque with it .Lousen the bolt on top and you can angle it left or right . The MOST IMPORTANT thing to check is every pert of that steering system .Check your cables , Pullies Everything top tp bottom .And where stuff is attached to the hull make SURE its solid .If any of it ever breaks that motor will slap sideways against the transom Now there a handling problem ...L.O.L..I had it happen once and dont ever want it to happen again . I feel lucky to be alive after that one ..Safety First ..
Take care
Larry

I disagree that 70hp is okay on a 14-footer. Not all hulls are created equally. What is your boat's rated horsepower max? I'm not saying that you can't tweak your set-up to make it work and I'm not against putting more power on a hull than it is rated for, but there are some hulls that simply get squirrelly when you put too much power on them, not matter what you do to counteract that. I'm not familiar with the PT-140, so I can't say one way or the other. Just keep in mind that even after you try the above suggestions, you may still have a boat that does weird things at speed.

As another suggestion, are you running with a kill switch and lanyard attached to your lifejacket? A 14-footer with 70 ponies qualifies as a go-fast and those items should be a given...

I have played with the trim tab and adjusted it all over, but it doesn't seem to make too much difference. As for the motor trim, it seems to want to be at the bottom two settings, or it cavitates out of the hole. The boat was rated for 60HP according to the original literature I found online, but that was in 1960. I know horsepower ratings have changed over the years. I didn't think the extra 10 would make too much difference though. Still not taking any chances, so I use the lanyard! As for prop changes, I will need to get a tachometer first. As for the hook you are talking about, if there is one present,are there any solutions? Or is weight distribution the key to counteracting it?

yes you can repair the hook but you need to measure the depression both diameters and depths to determine how best to approach the repair

Or is weight distribution the key to counteracting it?

no hooks can be dangerous if on one side and need to be addressed
if on 2 sides and symetrical it will slam the bow down and scrub off up to 30% of you top end speed..these old boats that have been sitting on trailers are the most common, especially roller style trailers

It almost looks as if there is one designed into the hull if you look at where the keel meets the flat part of the bottom. It is consistent on each side, about 4 feet long, at the keel there is a 1" depression, and as you go out to the edge, about 24" out, parallel to the keel it straightens out.

some hulls do have a hook built in them but they are perfectly symmetrical , not too many flat bottom hulls Ive seen do.I have seen alot of old hulls and thats were the hook is...from the weight of the 70hp motor on the trailer for 50 years ESPECIALLY when the bunks dont extend past the transom, with rollers it can almost be expected

does the boat fly the bow, where do you see the water breaking and splashing at the hull when your driving? upfront , beside you , behind you? or can you post a video or pics of the boat cruising speed and when you feel the problem,

I would say you need to fix the hook. First, how solid is the hull structure? Does it have stringers? If the stringers are rotted then filling the bottom won't matter. Once you determine the hull structure is SOLID, then you would need to flip the hull over and blue-print it. Filling and faring until it is symmetrical and straight.

The splash is right next to me while cruising. When I look back there seems to be a lot of flex in the boat.

The hook seems to be equal on each side of the keel. What you said about roller trailers is quite disheartening though, she was on one when I bought her. I ended up finding a snowco locally to replace.

When I replaced the floor, there were some stringers perpendicular to the keel that were all rotted out. They weren't fiberglassed in place or anything though. I replaced them, adhering with Sonolastic NP1. I then put the floor in, adhering with the same and screwing into the stringers. There were no stringers parallel with the keel, didn't appear to ever have been either.

ill just answer the easy question,lol,the way to remember port from starboard is "port"has 4 letters just like the word "left".
so left is port,and right is starboard.john

secondrowjoe wrote:

When I look back there seems to be a lot of flex in the boat.

That is NOT good. Flexing, particularly in a boat that is overpowered, can be a dangerous thing...

When I rebuilt my 15-foot Starcraft, I overbuilt the hull structure, with the intent that someday I may make it into a River Rocket of sorts. Beefier stringers, extra transom support, beefier transom, etc. It is ROCK solid. You may want to revisit what's under your floor to do the same. Add stringers, tie them into the transom, etc. You may be able to straighten the bottom from the inside in the process...

could we get a pic or 2 of this boat? it would help to know what we are working with.

secondrowjoe wrote:

The splash is right next to me while cruising. When I look back there seems to be a lot of flex in the boat.

you have a winter project, re-vist your structural work then fix the hook

If you have flex I's look seriously at the structural integrity. I seen more than a few old boats for sale with the transom busted down and out. You see them on Craiglist with such captions as needs TLC, minor imperfections, and needs polish. My keel was hogged out after years of use and bad support under the back of the boat. Since my keel was internal and wood I put support under the boat and left it soak with 6-8 inch's of water in it. After it went straight I took the water out and left it dry. Problem solved.

I will try to get some pics this week. I found a cheap single cable steering system here in town and am going to put that on. Then take it to one of the local lakes and give her a try. When I did the floor, I guess I just replaced what I found already there.

Here is a "beefed up" transom. Note the knee braces are thru the floor and attached to a stringer.

I have a new development in this saga. I was talking with a friend of mine about my boat and he told me he was trying to sell his old Owens. Said it was a late 50s 15' runabout with a 28hp Johnson on it. He said the Johnson wasn't enough motor for it. I was thinking of maybe picking it up and doing the ol' swaperoo with the motors. the 70 on the Owens and the 28 on the Silverline. He then told me his dad has an old 15' Tomahawk in his barn. How do you think either of these boats would handle that 70?