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I have a 1961 Cruisers Inc. Model 370 Royal Commander with a vintage 75 hp Evinrude Starflite IV engine that runs great. This is the long shaft version on a 20 inch transom.

The problem with this boat is that at speeds above about 15 knots this boat's steering becomes difficult to handle and unpredictable. Sometimes it won't want to turn and then suddenly it lurches into a turn. That can be quite frightning at 15 knots.

I have posted about this problem before and I mentioned that there was a slight hook in the bottom near the transom and also that a previous owner had installed a skeg running about 4 feet along the aft portion of the keel rising to a depth of about 6 inches. I presume that this skeg was installed as an attempt to cure the steering problem.

I followed the advice I received from this group to remove that skeg and deal with the bottom hook to cure the steering problem. I also tightened up the steering cables to increase spring tension and eliminate any play in the steering. Well, all that was accomplished and I just sea-tested the boat today. The boat still has steering difficulties at above 15 knots. In tight turns, even at speeds between 10 and 15 knots, I can hear the prop cavitate which, of course, affects steering in a turn. But at higher speeds, even going relatively straight, I believe the motor cavitates sometimes.

I have adjusted the engine trim up and down in an attempt to get better steering control. At the highest trim position, the prop cavitates all of the time. As I lower the trim, the steering problem seems to get worse at higher speeds.

I've dealt with the skeg and the bottom hook and I've tried all of the available engine trim postions. I've confirmed that I have the proper long shaft engine for this boat's 20 inch transom. I believe the steering spring tension is as tight as it should be. I don't really know what else to do.

Any advice would be greatly appreciated.

All the best, Jim

sounds like bow steer, bottom needs to be flat for at least 5 or 6 feet.

How does the boat ride when on plane? Does the bow ride out of the water? I agree with John, it sounds like the bow is still in the water. Especially if the motor is cavatating as you describe. You might need to shift weight towards the back.

I tend to agree about bow steer, if you have really cured your bottom hook.
I have owned several of these hulls and currently have a 570. These hulls are heavy forward, are your fuel tanks aft?
My the bottom of my 570 hull is almost flat from midship back, the 370 has a little more shape towards the rear.
These hulls are kind of like big canoes and weight distribution is very important. Move as much weight near the transom as you can and test.
If your hull has a serious hook it will dive the bow at speed.
You may need to get a long straight edge and lay along your bottom laps to check for any concave areas.

Thank you for all your contributions.

I believe that my bow doesn't come out of the water at higher speeds even with a 12 gallon tank in the stern and a couple of passengers sitting aft by the motor.

The bottom curvature that I reported several months ago seems to be reduced now that it is sitting on better trailer support. But, on closer inspection, there still seems to be a long shallow concave portion of the bottom running from about midships to the transom. The maximum deflection measures at only about a half an inch but I guess I should think about this as a half inch deflection of a trim tab that is 4 ft long and 7 ft wide.

I think I've gotten all of the spring-back that I can hope for from the hull so I'll need to do some additional bottom work. I have been thinking about adding a layer or two of CPES treated marine plywood in the area of the deflection and then fare it in to make the bottom flat. Yes this will make the boat a bit heavier but it will also make the bottom both flat and strong.

Does anyone have any comments about this approach to curing the problem? Are there any other approaches to consider?

Your advice is sincerely appreciated.

All the best,

Jim

A one half inch hog. That's definately your problem. That's a huge amount for this size boat.

How to rectify this problem is another question.

Andreas

The keelsons on this hull are probably permanently bent. We restored a smaller boat last year that had the same problem, we replaced the keelsons with double thick white oak and that removed most of the hog.
I have always thought that you could add a layer of plywood to laps and fair in to cure this problem. I have never tried it.
Check out these two links , there are parts that deal with bottom issues.

http://www.thompsondockside.com/views/v ... highlight=

http://www.thompsondockside.com/views/v ... php?t=3216

I have shimmed under ribs before to push laps out. I removed screws that ran through laps into ribs then the laps will push away from ribs. I pushed oak shims between rib and lap and re installed screws through shim to rib.

Good luck.

I would bolt an 6" I beam with about an inch of deflection on top of keel and slowly tighten it over 6 months or more till you have a rocker rather than a hook in the bottom. Keeping the inside of the boat wet might help as you slowly pull out the hook.

Andres, Dan, John and Ken,

Thanks for your comments that tend to confirm that the bottom hook is the problem and thanks for the various suggestions to cure or at least minimize the effects. It may take a combination of approaches to fix this problem.

I've read a bit more about how a hook in a boat's bottom is typically caused by trailer bunks that do not go all the way to the transom. I can see that over time, especially with a heavy OB motor, the aft portion of the bottom could sag beyond the end of the bunks.

In this case, however, this boat sat on a trailer that had a fixed keel support at about the middle of the bottom. It seems that the center keel support was set up too high or the bunks on the sides were set too low. So the curvature of my boat's bottom is not at the last foot or so of the bottom near the transom but is centered as much as 4 or 5 feet forward of the transom. This gives the entire bottom a long concave shape and the bow appears to jut downward like Jay Leno's chin.

The idea of using an I beam to pull the keel outward would be a way to work on such a long curvature without having to add a lot of material to fill in the bottom. But, is it worthwhile to attempt it? Has anyone had success pulling a keel to straighten out a hook? What about spring-back after the tension is released? What about potential damage to the keel or ribs?

I'd like to explore this idea but I don't want to cause any further damage to the boat. Any advice?

All the best,

Jim

Jim

I read somewhere about placing your wood boat on blocks in a garage and jacking against the ceiling to deform it back into shape, my beam idea does the same without jacking against the ceiling.

My proposed beam has curved so the bottom can be deformed into a hook, and with spring back would be straight.

Another possiblity, is using an alum beam with a slight curve to be installed permantly on top of the beam and left in place holding the keelsom stright. Beam could also to a bigger piece of oak. This idea may be the best and fastest, bending keelsom only 1/2 inch is just deflection, in the range of normal stressing, and just holding it there with extra sistered beam either wood or metal, allum being the lightest. Over time the keelsom will bent back straight, just as it deformed hooked.

Your hull could also suffer from power hooking, basically as more power is applied the keelsom hooks more, if this is the case sistering a stronger keelsom will help you even more.

Look at my pictures of my Cruisers 202 and my replacement keelsom, my bottom is now straight. www.aerialimaging.net/john

I did do considerable work after my new keelsom, fairing my bottom straight, biggest gap might have been 3/16" filled with expoxy puttty. Still good at 6 years and 150 hours and 9000 miles of trailering. One of my pictures show my boat runs full power with most of boat out of water at 40 mph+ with a 75 Evinrude.

John,

Thanks for the link to your pictures. I can see by the shape of your keel that the curve from the bow transitions into a straight keel running aft. Mine has a dip at about the mid point of what should be a straight keel.

I happen to know someone locally who is a professional vintage boat restorer in our area (Lake Dora, Florida) and I've watched him replace keels and ribs on several boats. It's too big a project for me but I'll explore what it would cost to have the keel and bottom replaced professionally.

If that is too much money for me right now, I'll probably try to pull the curve straight. It might be possible to use the location on the trailer that held the center support to pull the keel downward in the same location.

All the best,

Jim

Jim

If you used the trailer to help pull the bottom straight by drilling thru the keelsom and pulling the bottom past straight and then sistering a larger keelsom to it would probably work.