Issues with new-to-me 93 Gulfstream

[gwwannabe]

Hey guys.
Finally got the new boat out for a good sea trial. The guy I bought it from was very up front about his frustration with the motors. They are twin DF140s - 140 HP four stroke Suzuki's. He had been researching going to 4-bladed props in order to stay on plane at lower RPM. The existing 3 blade props are 14X18's according to him. In moderate seas - 1 to 2 footers, the motors hit 6200 rpm very easily. I'm convinced that it needs more prop.

This past Saturday, we took it out into the Chesapeake for a ride down to Wolftrap Light and back. Strong southerly winds had a 3-4' chop running and hitting us off the starboard bow. Going out I had to stay above 4,ooo RPM in order to stay on plane. Boat handled the seas wonderfully and we passed several boats on their way there.

Once we rounded the lighthouse and headed back, it became much more difficult. To stay on plane I had to stay up around 5,000 RPM but this was too fast for conditions. Back off toward 4000 and the stern sank and we just wallowed.

Once we got back into the river and out of the chop, I found that the boat liked 5,000 RPM for cruising best. Back down toward 4,000 and it started getting stern heavy. Under 4,000 and it was wallowing. The boat has Bennett trim tabs but frankly, I could not see any effect from them at all. Trimming the motors up made a noticable difference.

I spoke with the Suzuki dealer nearby and he recommends going up to 14 x 19s or even 20s AND adding Dole fins or similar products to the motors to generate more lift.

I spent several hours researching props on this site and another yesterday and noted recommendations of a prop shop in Chesapeake. I plan to contact them soon.

I would love to hear your opinions about my prop situation and especially about adding Dole fins or the like. By the way, I LOVE the new boat.

Gary 93 Gulfstream

 

[twobyfour]

Don't know about the dolefins.. But if you can't tell a difference between tabs all the way up and tabs down, then they are either not working or are to samll for the boat.. Four blade props are the way to go as long as your not worried about top end speed, which you should not be or you would have bought a speed boat..

 

[Tuna Man]

I spent a lot of time on a 2000 Gulfstream with a single Yamaha 225 2 stroke. The boat appeared to have similar problems as you just encountered.

First thing the owner did was increase the size of the tabs from 12w x 9? to 18w x 12. This helped out tremendously in keeping the bow down in anything over 1' seas. I assume with twin four strokes the boat would have more of a tendency to run bow high, so the larger tabs would certainly help keep the bow down.

I have not been on a Gulfstream with twins, but I would assume that you should be able to easily plane and slow cruise at around 3800rpm with a clean bottom and average load. Most Gradys I have been on or read test reports on seemed to be most efficient (when propped properly) at about 4200 rpm. At 5000 rpm you will often go faster, but consume nearly 1.5 times the fuel.

It appears that you need either different props or the engines are mounted improperly. You did not mention what speed you are running at 6200 or 5000, this would help determine what is the cause of the problem.

One more idea. You may want to change the way you load the boat, you might find the helps. Assuming the engines are not too heavy for the boat, were you carrying a lot of weight at the stern of the boat? Was the forward fuel tank empty and the rear tank full by chance?

Hope this helps a little. By the way, congratulations on the new boat!

 

[gwwannabe]

Thanks for the replies 2x and Scott. I just came back from the boat where I checked on the movement of the trim tabs. They only moved about 2 inches. The fluid resevoir was more than half empty. Filling it proved to be a real challenge. The instructions on the unit and in the owner's guide says "remove Lexan cover". Didn't say to remove the screw in the top center. Was very difficult to see it and even harder to find something that would fit up there. Finally got it. Then, finding something to pour fluid into that tiny hole was a challenge but finally got that, too. What a pain! Next time it will be a lot easier. The fact they were not working explains some of the problems I experienced. The question now is where the fluid went and over what timeframe.

Scott, we were very lightly loaded when we went out. There were 2 men and 2 women. There was around 50 gals in the main tank and around 25 in the aux tank. There was some water in the fresh water tank but don't know how much. I have perhaps a 150 to 200 lbs of stuff in the cabin.

The prior owner emphasized that the boat is slow. When we were turning around 5k rpm on the smooth river, I think we were only running around 26 knots. WOT at 6200 only sees about 30.

I checked the trim tabs - they are 12 x 9's. Bigger tabs is an intriguing idea and I bet it would help. I'm thinking that getting the props squared away should be the first priority tho' - anyone agree or disagree?

Again, thanks for the input - I really appreciate it.

Gary

 

[3rd Day]

Enjoy that Gulfstream!!! I love mine.

 

[BobP]

That's a heavy boat, and smaller motors. You need plenty of trim tabs to do anything except WOT. Watch your tabs in following seas. And make sure motors are trimmed properly, up or down too much is no good. Prop blade shaft to be parallel with water surface at speed.

I don't bother trimming motors when taking off, so it takes longer (wallowing), I just blast the throttle and climb out of the hole with 400HP power on. If you trim down on acceleration, it will help, but readjust at speed.

Avoid use of aux tank if you have one, load main.

Any speed other than planning especially just off plane, use tabs to lift stern otherwise the stern will seem like it is plowing a field.

And just let it take it's time to get on plane, nothing you can do about it. The 4 strokes and lower HP just don't have the torque to do it faster - so wait.

You can underprop to gain more torque but top speed will drop and need to avoid going over WOT in use. But nothing wrong with it.

I think that model was rated 400 or 450HP max. Would be much different with twin 200s or even twin V6 150 2 strokes.
With twin 200s would be a 50 MPH boat.

 

[Grog]

Things just don't seem right. The DF140's weigh in the low 400's so they're similar to the 150 2 strokes. At cruise there isn't going to be much difference. It should have similar performance to a boat with a single 250 which people have said is no rocket but not that bad. You shouldn't have to run them that hard to get the boat to plane. Where is the cavatation plate when the boat is on plane? The motors may be too low causing too much drag. Also if the motors hit redline very easily, they aren't propped correctly. The correct props will give more lift and drop the cruising RPM's.

If you have a bracket is it full of water?
Are you sure the 2nd fuel tank is empty?

 

[gw204]

Every bracketed Grady I have put my eyes on had the motors too low. On my old 252G, I was able to raise the engines 2 notches.

It also sounds to me like your problem isn't with getting the bow down, but getting the stern up. Had the same problem in the 252G. A nice pair of Mercury Mirage Plus props fixed that for me.

After raising the motors and changing the props my boat performed like an entirely different rig.

 

[gwwannabe]

The more I get to play with it, the more I like my Gulfstream. I'm convinced that it's under-propped so I've decided to explore that avenue next. I spent a couple of hours on the phone with Bay Propellers yesterday and the recommendation was a 14x18 4-blade prop was the place to start. Only problem is, he couldn't get a counter-rotating prop for my I-4 motors so I may have to gamble and buy the Suzi props at $650 a pair which isn't bad but not pocket change either.

In the interim, I'm going to send my props down to Bay and they're going to true them and put a cup in the blades which should help some. Only $75 a prop for this so hopefully I'll have a decent set of backup props when this is all done.

The prior owner told me that the main tank is to the rear and the aux tank is forward. For normal usage he'd keep the main near empty and just fill the aux tank so the weight would be forward. As it is right now, the aux tank is near empty and the main is about 1/3 full.

Since the boat was trailer-kept for the last 3 or 4 years and is now lift-kept, I didn't think about the bracket perhaps being full of water. I'll check it out.

I haven't checked where the cavitation plates are when under way but the heads seem to sit awfully close to the water. My local Suzi dealer, less than 5 miles away, wants to check the rigging out. I'm going to try to get him to come to my place and go out on the boat. Love for him to see it in action.

Gary 93 Gulfstream

 

[Grog]

A future option may be to change to a floataion bracket. With the extra bouyancy it will not matter which tank you use. I have one on my Sailfish and it's tough to get the stern to squat. But see how she goes with the props first.

 

[gwwannabe]

Took the Gulfstream out for a cocktail cruise this evening and got to play around a bit. First thing we did was track down a really obnoxious vibration when running on both engines at idle or slightly above. The vibration is in the port side window where it attaches to the windshield. The top screw is stripped so that connection is not tight. I wedged some paper in there to quiet it down but I need to fix it right. Anyone had to deal with this?

OK, while out there I checked where the cavitation plate was when running at about 5k rpm. The plate is at least 4" below water level, maybe as much as 6". And this was with my Bennett tabs down to provide lift. Brian, I think you nailed this one. I hope to talk with my Suzi dealer tomorrow about changing this.

Checked the speed again on the river in virtually flat conditions tonight, also. At 4800 RPM we were doing just under 22 knots. Any lower rpms and there is all kinds of spray coming off the motor and the sides of the transom, guessing the trim tabs. Need to get those motors up and also get the stern to ride higher in the water.

Appreciate all the help.
Gary 93 Gulfstream

 

[SouthPass]

4 blade

My 93 Gulfstream will run on plane at 3700 rpm 27mph with twin 150 evinrude on bracket with 4 blades. Big difference out of the hole, planes very well loaded 180 gallons fuel 6 people. Top end is lower but not an issue.