Bravo 1 planing problems

[Scaffoldmaster]

Gentlemen,<br /><br />I have a 1991 Thompson 26' flybridge fishermen. It has a 7.4 454 mercruiser with the bravo 1 drive.I would estimate the boat weighs around 8000 lbs. It has a 10'2" beam. I can't seem to get the boat on plane, it has good bottom paint, the wot range is good for the specs. 4200 rpm. I replaced the prop to a 4 blade. I have to hold the boat wide open or it slips back in the water. It's not good to hold the boat at 4200 rpm for any duration. The boat has no speed whats so ever. The gas milage is terrible because i'm pushing the water, the trim tabs work well but they push the nose in the water under full throttle. Would the bravo 2 be a better application with the bigger prop diameter and more torque for this boat. Your advice would be appreciated.<br /><br />thanks,<br />scaffoldmaster

 

[steelespike]

Re: Bravo 1 planing problems

I wonder if there is water intrusion into the hull or flotation somewhere.Its a big boat but it sure seems to me it should stay on plane easier.I have a friend with a 26 Sea Ray, no fly bridge with a smaller motor and remote trim tabs It planes easily and stays on plane with little effort.

 

[Bondo]

Re: Bravo 1 planing problems

Ayuh,.......<br /><br />I'm Sure there's some Issues with your boat,........Other than Which model outdrive is on it........<br /><br />That boat Should "Get Up,+ Run",.......... Even with an Alpha drive..........<br /><br />You say it has "Good Bottom Paint",......... How much Crap is hanging off it,......... That you Can't See........

 

[Scaffoldmaster]

Re: Bravo 1 planing problems

I pulled the boat out of the water a month ago, the bottom is clean, it has the blue bottom paint that will turn your hands blue if you rub on it, nothing sticks to it. I pull the boat out a least once a year for maint. pressure wash the bottom and change outdrive oil and zincs. I have a tripple axle trailer, so its no big deal to do. There is no water in the hull or engine compartments. The engine runs good, no missing or mechanical problems. When I bought the boat a year ago, it had a stainless 3 blade mirage prop, it turned 5000 rpm at wot. I went through a prop house and bought a 4 blade aluminum with a different pitch, the boat stays at 4200 rpm at wot now. It feels like its burning out in the water when I stand on it. the back sags down and it doesnt feel like it is grabbing the water. I do not feel the front in nose down like other people. It would be nice to get it on plane and have it stay there at 3000 rpm.<br /><br />Scaffoldmaster

 

[Mischief Managed]

Re: Bravo 1 planing problems

Maybe the hub is shot on the prop. <br /><br />'Nuther thought, is the prop hub diameter the same as the lower unit gearcase diameter? If the prop hub is smaller, exhaust gases can escape into the blade area of the prop and prevent it from hooking up.<br /><br />I had this problem with a 4 blade SS prop I bought on eBay. I fixed it by fabricating a collar to fit around the hub and block exhaust gases. Worked exceptionally well after that, increasing the top speed of the boat and making the holeshot better as well...<br /><br />The prop and fabricated collar

 

[tommays]

Re: Bravo 1 planing problems

You really need a prop that lets you reach your motors top recomened WOT.<br /><br />i am sure its more than 4200 and running it this way just makes the motor work way to hard.<br /><br />What was the problem with the orginal prop that had the 5000 RPM WOT ?<br /><br />You have trim tabs BUT how are you triming the drive and tabs ? <br /><br />It sounds like everything is to far down and just plowing the bow <br /><br />tommays

 

[Reel Poor]

Re: Bravo 1 planing problems

What diameter and pitch prop are you running on it now?<br />What diameter and pitch prop did you remove.<br />Has it ever performed the way it should sence you've owned it. <br /><br />If not:<br />Maybe someone has installed the wrong gear ratio drive on it.<br />Maybe the transom has some rot issues and is flexing under a load.

 

[Scaffoldmaster]

Re: Bravo 1 planing problems

Thanks for the response guys, <br />The wot spec for my boat are 4200 to 4400 rpm, Tommays, 5000 rpm is too much for the big block, thats why I changed the prop. When I come out of the hole, I put down the trim tabs and stand on the throttle, as the boat feels like its planing, I back the tabs back up and start easing up the throttle and the boat falls back in the water, pushing water. I have never tried to trim with the outdrive, I have heard it was bad for the drive. Mischief, the prop diameter is the same as the drive, the hub is new, I just greased up the splines. Mr Reel poor,the prop diameter I removed was a Quicksilver s.s. 15.5 diameter 17 pitch,3 blade. I installed a Michigan 15.5 19 pitch 4 blade. The prop house said this is the ticket for the boat. I believe the gear ratio in the bravo 1 is 1:50 and the transom is fiberglass, I'm not sure about the flexing. I'm still wondering about a Bravo 2, with the bigger prop for this application.<br /><br />Thanks

 

[tommays]

Re: Bravo 1 planing problems

S<br />There should be trim limits on the drive that will keep it in a safe running range when you raise it up .<br /><br />When its all the way down its below level and pushing the bow into the water to help you get started.<br /><br />After you get going it will need to be trimed up to allow the bow to rise up and not plow through the water.<br /><br />IF you trim it to high you will start to get some prop cavitation and you will know you went to far.<br /><br />The combo of trim tabs and drive trim are going to take some time to find the best settings.<br /><br />It might be helpfull if you can find someone in your area that has some time with a setup like yours to point you in the right dirrection.<br /><br />tommays

 

[QC]

Re: Bravo 1 planing problems

Are you sure the tach is right? This is always my first question. Seems like 800 RPM is a huge difference between those two props. When it ran 5000 RPM did you get higher speed? If so, I would suggest this is not a horsepower issue as the horsepower should be falling off up there. Regardless, I am not sure why you think it is the drive Also, I think the spec is 4200 - 4600. I would try and get closer to 4600 RPM after you verify the WOT range. I don't recall a Merc with only a 200 RPM range . . .<br /><br />I also think you are messing up with your trim and tabs. I would start with the trim all of the way down and the tabs all of the way down. I would not play with either until the boat has stopped gaining speed at WOT. Then I would make very slight adjustments in a variety of combinations and see if there is any improvement, if not go back to the last good setting and try something else.

 

[Always Broke]

Re: Bravo 1 planing problems

I deleted my last post and did a little research that might help ya. Here’s a link to a prop calculator for Mercury propellers http://www.mercurymarine.com/prop_selector When I put your info in it looks like you would want anywhere from a 15” to 17” pitch depending on which type of prop you want. They are not giving diameters but are giving the factory part numbers for the props. That will at least put you in the neighborhood of what you want, make sure you take your hull configuration, weight distribution, etc. into consideration.

 

[paulie0735]

Re: Bravo 1 planing problems

What was it like with the old prop? If you’re only pulling 4200 than the prop is too big! Going from a 17" 3 blade to a 20" 4 blade is to big a jump, my information is that the 20" 4 blade is more like 21" in a 3 blade so you have gone up to much. You need to get the bow up and out of the water to reduce the drag, the outdrive is built to use the trim, sure your boat is on the large side and will likely not respond to trim like a smaller boat but its still an important part of the setup and will have a big impact on the way the boat performs. Changing the drive will not solve your problem. Going down an inch in prop size and using the trim and tabs correctly to get the bow up and out of the water probably will. Also, how is your weight distribution?

 

[Scaffoldmaster]

Re: Bravo 1 planing problems

Paulie,Always broke <br /><br />Your point is well taken. I changed a 17" to a 19". I'll check the wot again, it might be closer to 4400 to 4500. The problem with the boat is that the front in feels like it is too far out of the water and the stern is too far in the water. If I use the trim tabs it pushes the nose down but the boat is not on top of the water, rather in it , pushing the water. I will be honest and say I am not sure how it should feel to be planing with this boat. I have been on other boats when the nose rolls over on plane and keeps planing at 3000 rpm. This boat falls back in the water and steadly loses speed unless I'm wide open. I would say much heavier on the back with the 454 engine and 120 gals. of gas.<br /><br />Tommays & QC,<br /><br />It might just be operator error with me driving the boat. I like your advice with the drive trim, I will give that a shot. Will raising the trim slightly bring the stern more level on plane? I understand the front has to be up to get on the water but once it start planing I have seen boats on top of the water.

 

[tommays]

Re: Bravo 1 planing problems

S<br />First play with the drive trim with the tabs all the way UP you should be able to plane fine with the drive trimed to the correct level.<br /><br />Then you can find out your WOT with out the bow plowing.<br /><br />When you get comfortable with triming the drive you can start to use the trim tabs to help the boat plane at lower speeds and see how the drive trim and tabs work toghter.<br /><br /><br />tommays

 

[Always Broke]

Re: Bravo 1 planing problems

Like Winston Churchill said: "Americans will do the right thing after they've tried everything else". If the prop and trim tabs don’t work to get this boat to perform the way it should and your still having problems I think I’d start looking into the motor. This thing should be putting out around 330 HP and the big blocks are noted for their torque on the low end, which you seem to be missing. You got the boat a year ago and who knows what was done to the motor before you got it unless you were lucky enough to get a service log with the boat. The motor is running OK but there’s something missing, mid range power. You may be trying to make up for an engine problem with the prop. An engine does not have to have a miss in it to not run properly. If every thing checks out OK on the motor, (compression check, timing, etc…) I’d check the cam to see if someone might have changed it possibly putting an automotive cam in it, sure it will run fine if they did but the power curves are different, your pushing a lot of boat there and you need as much power as you can get in the lower RPM range. Well, just thought I’d try to look at things from a different angle.

 

[paulrfrancisco]

Re: Bravo 1 planing problems

Scafoldmaster, the michigen prop you went to... was it new or a remanufactured prop? I once had a prop shop swap out a damaged aluminum prop with a like geometry, same make, prop and the boat ran horribly... in fact worse than the damaged prop...(curled blades) so I took it back and had it exchnaged. The replacement was like day and night... So the point I make here is it could have been a poor reman job. Could be you started with the incorrect porp, and switched to one that is poorly refurbished.

 

[Reel Poor]

Re: Bravo 1 planing problems

Originally posted by Scaffoldmaster:<br /> When I come out of the hole, I put down the trim tabs and stand on the throttle, as the boat feels like its planing, I back the tabs back up and start easing up the throttle and the boat falls back in the water, pushing water.

Just a thought, and might be out of place, but some people think that trim tabs are wired backwards and do not operate properly by the switch. Properly wired, the switch when pressed at the top will cause the bow to be forced down (into the water). When pressed at the bottom will alow the bow to rise (out of the water). My thought is you may be running your tabs down (into the water) as you throttle back. This would cause the boat to plow and fall off plane.<br />Look at the switch closely it should be printed as follows:<br /><br />Top of Left Switch......Port Bow Down<br />Top of Right Switch.....Starboard Bow Down<br />Bottom of Left Switch...Port Bow Up<br />Bottom of Right Switch..Starboard Bow Up<br /><br />Simply stated the switches tell the bow how to react, not the tabs. <br />Remember Bow Up or Bow Down

 

[paulie0735]

Re: Bravo 1 planing problems

reel poor, now its that kind of thinking that makes us all that bit smarter!

 

[Scaffoldmaster]

Re: Bravo 1 planing problems

I would like to thank everbody for their advice on my problem. <br /><br />Mr Reel poor,<br /> My trim tab switches are clearly marked as you descibed, plus I checked their operation when I had the boat out of the water last month.<br /><br />Mr Paul,<br /><br />The Michigan prop I purchased was new, The prop actually worked better and dug in where the old prop felt like it was peeling out in the water at the hole shot.<br /><br />Always broke,<br /><br />Your advice is good, I recieved every reciept for this boat since it was built. The guy kept extremly good record keeping plus he kept a log on performance and servicing. It was never logged about the problem of planing so I still believe it is trim control or lack of it.<br /><br />The motor is clean and strong, it has 630 hours on it. I gave it a compression test myself at purchase and it only had 3 pounds difference between all cylinders. I pulled the valve covers off and checked for oil gunk, which ther was none. There is no rust on the engine and there would be no reason to change camshaft unless there was a rounded lobe, plus no reciept for that work. The guy I bought the boat was not very mechanicaly inclined but had buku cash for repairs when needed, mostly preventive maintaince, he always took the boat to the same shop and used his business account in which he owned the business. Money for him was not a issue.<br /><br />I am taking the boat out this weekend and I will report how it ran with the trim changes.<br /><br />Thanks to all in advance.