Re: [OMC-Boats] OMC Stringer trim

From: lib1@...
Date: Tue, 24 Jun 2008 20:24:39 -0600

 As far as trim tab options go there are three that I know of: (Hydrauic) (Electric) (Auto)

All of these will help get the boat out of the whole faster (especially when popping up a skier or wakeboarder). I have the Bennett's and they do a good job of reducing the porpoising effect by bringing the bow down essentially by pushing up the stern. They create a lot of force so be sure you think thru the structural integrity of the mount points.

> There appears to be some degree of adjustability in the front engine mount. Has anyone tried to re-trim using this feature? I know from past experience that sometimes a very small change in thrust angle makes a big difference in boat dynamics.

You can adjust the front engine-to-floor mounts, (I think there are 3 or 4 holes) and change the static thrust angle or trim. Problem is what's good in one case probably hurts another, so it is a compromise of sorts. No harm in trying, but I think you are likely not going to see much difference, unless you have an ideal situation to control and repeat your testing.

On the 1970 and later 16-foot hulls there is a sealed under floor water ballast compartment and I suspect that since your bilge isn't working you are getting more than a normal amount of water in there. The ballast compartment was a safety design issue. OMC designers were years ahead of the boating industry. OMC boats begining in 1962 with the 17-footer were the first in the industry (along side Boston Whaler) to remain totally level when fully swampped and carrying their rated passenger load. I believe the ballast water "tank" is designed to help balance the bow/aft attitude if your boat becomes totally or partially swampped. Most boats of that era were prone to swammping bow high. OMC designers were sensitive to the porpoising problem and they juggled fuel tank locations on different designs to try and provide the best balance. Didn't mean to scare you -- the water under the floor is most likely not getting into the foam -- most likely it goes into and comes back out of the ballast tank as you describe.

Bottom line you probably want to get a auto-switching (working) bilge pump ASAP. That will take car of any minor water that always seems to get in there. I'd go for modern, seperate units, rather than the combined bilge pump/blower that OMC used. Not pumping out that bilge automatically is most likely contributing to the porpoising problem and it can't be good for fuel economy or performance either. And you for sure want to get a decent bilge blower to ventilate the fumes before starting the engine.


----- Original Message -----
To: <omc-boats@...>
Sent: Tuesday, June 24, 2008 11:42 AM
Subject: [OMC-Boats] OMC Stringer trim

> Great information, Lee, thanks a million. My companion did suggest the "slow down" option a number of times, but that didn't seem too desirable to me! I think I may investigate the trim tab addition, as that seems like a fairly easy solution to getting some degree of trim.
> There appears to be some degree of adjustability in the front engine mount. Has anyone tried to re-trim using this feature? I know from past experience that sometimes a very small change in thrust angle makes a big difference in boat dynamics.
> You mentioned an under-floor water issue. I shipped a fair amount of water during several hours (maybe 20 gallons?) not sure where it came from, but the bilge pump wasn't working and a lot came out the plug at end of day. There seems to be a small opening at the bottom front of the bilge. Can water get into the foam through that opening? Is that harmful to the foam or the boat structure? Has anyone attempted to seal said opening? I assume it's nice to give water a way out if it should get into that space, but it'd be nice if bilge water didn't get in there.
> One other thought on that water in the boat. I just noticed that the blower outlet is right at the beltline, behind a piece of trim. It seems that following seas could likely get that high and admit a fair amount of water. Has anybody else seen this as a problem?
> I need one of the forward-facing aluminum vent scoops for my boat, the ones maybe 1-1/2" tall, 5" wide, and 10" long. Does anybody have one of these?
> Bob
>> Hi Bob,
>> Good to hear about your experiences. I have a 16-ft Evinrude Sportsman
>> (a similar hull configuration to yours) and can offer my
>> "for-what-they-are worth" observations:
>> 1) Be thankful you have the last hull design OMC released in 1970. It
>> incorporated a 4-inch deeper dead rise by extending the keel over
>> earlier (1964 - 1968) versions of the same 16-foot Johnson and Evinrude
>> hulls. You boat may have the new-for-1970 water ballast tank under the
>> floor. Check to see if you are carrying any excess under-floor water
>> (weight). The rougher ride is Gull-Wing the trade-off for better
>> stability. Deep Vee's are better at cutting thru the rougher stuff but
>> are less stable and can be susceptible to chine-walking (lateral
>> movement underway). Yeah, my better half always complains, "can't we
>> slow down?" Especially rough are the seats the closer to bow you get,
>> where the up/down motion is more pronounced.
>> 2) The propensity to porpoise is also pretty common on these boats.
>> There are some cures -- some more practical than others:
>> a) Back off the throttle and slow the boat down, to the point of
>> stopping the unwanted oscillations.
>> b) Add electric or hydraulic transom mounted trim tabs that allow you to
>> adjust the attitude for load, speed and see conditions. Does your boat
>> have the small, aluminum fixed tabs?
>> c) some people have reported adding a hydro-foil on the sterndrive's
>> anti-cavitations plate, reduces proposing (personally haven't tried
>> one).
>> d) Do everything possible to lighten the aft-end of the boat. I won't
>> suggest practical ways to this but anything you have back there
>> contributes to the problem.
>> Lastly, DO NOT TRIM out the STRINGER outdrive. Many people sadly did.
>> The balls gears were not designed or intended to drive a raised lower
>> leg under power except for minimal, shallow water use, at idling speed,
>> (and even then I hate to even do that). To overcome the power trim
>> limitation OMC eventually added a hydraulically driven jack lift under
>> the lower front engine mounts. These were primarily offered on the
>> short-leg Ford V8's and the inline Chevy's. I think retrofitting one
>> under a GM V-series (Buick V6-V8 or Small Block Chevy V-8) would prove
>> to be difficult and not very useful. If you go the transom-mounted
>> movable trim tab rout, be sure and check that you boat's transom is
>> reinforced, as it can generate some serious forces and some of these
>> boats had very thin transoms.
>> Lee Shuster
>> Salt Lake City
>> ________________________________
>> From: omc-boats-bounces@...
>> [mailto:omc-boats-bounces@...] On Behalf Of mckeown
>> Sent: Monday, June 23, 2008 10:18 AM
>> To: omc-boats@...
>> Subject: [OMC-Boats] OMC Stringer trim question
>> I finally got my '71 Chris Craft Gull Wing 155 out yesterday after
>> owning it for about a year and a half! Fun boat, but it seems to ride
>> pretty rough on choppy water. Cheatham Lake (Cumberland River through
>> Nashville) where I was riding has heavy boat and barge traffic. We were
>> constantly pounded by wakes, even from small boats, and swells behind
>> the bigger boats. My companion, new to boating, wasn't too wild about
>> the ride.
>> The boat seems to porpoise readily on fairly minor swells. The normal
>> solution to this problem is to change the thrust angle by adjusting the
>> position of the stern drive in. Can you make this sort of adjustment
>> with the Stringer outdrive?
>> I discovered one unexpected advantage to owning a vintage boat - I
>> seemed invisible to the TWRA boat police. I think they figure that an
>> old fart like me in an old boat probably knows enough to have the right
>> equipment!
>> Bob
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Received on Tuesday, 24 June 2008

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