posted 01-17-2008 12:46 AM ET (US)            

It sounds as though your boat is not propped correctly. Please give us the following information:

- Your best top speed with the F250s

- The engine speed at Wide Open Throttle (WOT RPMs) at this speed

posted 01-17-2008 03:31 PM ET (US)            

What year is the boat?

posted 01-17-2008 05:52 PM ET (US)            

I believe your hull does not have a keel that runs to the transom. The full hull stops about 2 to 3 feet short of the transom. As such, the boat will be sensitive to where the weight is loaded because the weight of the motors is not supported well.

posted 01-17-2008 10:58 PM ET (US)            

Based on what you are reporting I am assuming you have Yamaha 14-1/2" x 19" Painted Stainless Steel propellers, part numbers 61A-45974-00-98 & 61B-45974-00-98. These propellers do not use any vent holes.

The PVS system is a vent hole system found on Mercury propellers. At any rate, you do not want to have vented propellers at all. If you try any Mercury propellers with the PVS vent holes, be sure to use solid plugs.

I agree with Peter's advice, try a pair of Mercury Revolution 4 propellers in the 14-5/8" x 17" size (with solid vent plugs.)

A large boat like yours is going to need as much blade area as it can get. The 14-1/2" x 19" Yamaha Painted Stainless Steel propellers are good props in their own right, but they are not going to be enough for your boat.

posted 01-18-2008 07:25 AM ET (US)            

I had a similar problem with my 27 Whaler WD with all the three blade propellers I tried. The 4-blade propellers cured that. I currently run the 14 5/8 x 17 Rev 4 propellers with the vents plugged.

If Alfredo switches to the 4 blade propellers, he may also notice that the venting while underway, sometimes called "blowout", typically caused when the boat rolls about the keel from port to starboard or vice versa causing one of the engines to be lifted high in the water, is greatly reduced if not eliminated.

posted 01-18-2008 09:31 AM ET (US)            

Tom Clark knows far more than I do regarding these things. However, I can tell you that I am "in the same boat" as you are. I have a 1998 285 Conquest. It has 2004 Merc. 225 4-strokes. The prior owner had installed them before I bought the boat. When he took me on a sea trial, the boat had less than 1/2 tank of gas, so it planed fine.

After owning the boat for a while and loading it up for long trips: 298 Gallons of gas, full water holding tank,
full live well, loaded with gear and passengers, etc. I began to experience the planing problems that you have. Peter hit the nail on the head. On our boat, the hull is notched and stops about 3 feet shy of the transom. I believe that our boat was designed with 2-stroke motors in mind. They are lighter and have a more powerful hole shot to get you up on plane. Check the specs on the weight of the engines that you had vs. the weight of the new ones.

If your Mercury was a 2000 225 2 stroke, it weighed between 482 to 500 lbs. If your Yamaha is an 07 4-stroke, it weighs between 592 to 608lbs. With twin motors, you have a minimum of 184 additional pounds and a max of 248! additional pounds hanging off the transom of your boat. That's a HUGE difference. Picture a 248lb man laying across the top of your outboards while you are trying to get your boat on plane. That's what you've got going on.

I agree with all of the guys regarding the Merc. Rev 4 17 props. I have tried 3 blades and there's no comparison. The Rev 4's are the best props for the setup that you have. I disagree with Tom regarding the solid plugs. I originally had the solid plugs on my Rev 4's and switched to vented plugs. My boat planes faster with the vented plugs. On Merc's website the PVS system vented plugs are used when your boat has difficulty planing (which is your problem). Speaking from personal experience, they worked better on my boat than the solid plugs did. They give the exhaust ventilation which allows the props to spin faster when you are trying to get on plane. The difference with the vented plugs over the solid plugs was certainly not dramatic, but it was noticeably better.

Although your boat will perform better with the Rev 4's, you're not going to get back the hole shot that you were accustomed to with the 2-stroke opti's that you had. However, it will be queiter, less exhaust and much better fuel economy.

When getting on plane with that rig and the Rev 4's try this. Trim engines all the way down and hit WOT, after about 6-8 seconds, tilt the motors up slightly while remaining at WOT. This should kick you up on plane. After trying lots of diffrent things over the past 2 years, this method has worked the best for my setup. Also, make sure that your trim tabs are all the way up (flat against the hull) when you are trying to get on plane. At low speeds, they will just create more drag on the stern of the boat and prevent you from getting up on plane.

Something that you may want to consider, our boat has a very large gas tank with a 298 gallon capacity. It was designed for 2-stroke motors. With your 4-strokes, you will not burn nearly as much fuel. I dont know how far you are going on these diving trips, but you may want to consider starting off with 3/4 of a tank of fuel. By doing so, your boat would be 487 lbs. lighter. You will still have about 223 gallons of gas, which will carry you very far with a pair of 4-strokes.

Best wishes,

posted 01-18-2008 01:54 PM ET (US)            

I would defer to Peter on that. I stand corrected. I was basing my statement on my impression that the average older model 2-strokes were less fuel efficient than the newer model 4-strokes.

My point is that the boat has a large fuel tank and a great range. Unless taking very long trips, you may not want to top off the tank. It's silly that not topping off the tank has to even be a consideration and it shouldnt be. But on that boat with 4-strokes, loaded with fuel, passengers, dive tanks, etc. etc. Sometimes it's not a bad idea to drop some wieght where you can. Even by filling up less 1/6 of a tank (50 gallons) is taking 325lbs. out of the equation when trying to get on plane.

Dont get me wrong, when I leave on a long trip or if I am trying to make a crossing to the Bahamas, I am loaded to the top with fuel, in the event anything goes wrong. However, for short offshore trips I'll go out with 3/4 tank 223 gallons.

posted 01-18-2008 02:20 PM ET (US)            

Since I live in guatemala Central America I already ordered the propellers from MC Marine in Miami, They are sending the Rev4 14 5/8" x 17" with the closed plugs. Since I used to have a pair of the 225 Mercury Optimax I have several set of plugs that I can play with.

Regarding the use of the boat we usually travel to Belize´s Atoll´s to dive and fish. I usally take my family (5 persons including me) and spend some days there. We stay in those small hotels out in the cays. We carry diving equipment, 2 big ice chests with ice, full water, full gas, sodas,beer and luggage etc... When I mean fully loaded is fully loaded. The problem in Belize is that there is no gas in the atoll´s so it´s vital to be able to plane in full load. From where we stay we have to travel almost 50 nautical miles to the closest gas station. We even sometimes take gas in drums, which I particularl don´t like.

I agree with Peter. the 225 optimax where more fuel eficient that these Yamaha´s I used to run the boat at 4600-4800 rpm at 30 knots burning 30 gph now I can´t obtain 1 knot per gallon, Hope this will get better with the new propellers. The yamahas are nice and for me was the natural choice as it turns that is the only brand more less well supported. the mercury dealer don´t know anything about the injection engines and I could´nt even get the sprark plugs for the engine. Its a shame because I believe that the Mercury engines are really nice but as they say a brand is as good as the support you can get.

posted 01-18-2008 05:04 PM ET (US)            

Tohsgib is correct on this. The upper part of the motors, shouuld only be an inch or 2 above the transom on your boat. That's how mine is. If they raised it up too high, it's a big problem because of the notched hull. Your props will be spiining in "wash water" created in the notch area and not be able to "bite" into the water and get you up on plane. On my particular rig, the engines are mounted as low as they car be.

A simple way to explain it is this. Stand on inside the stern of your boat and lean down and look at the engine covers. The top of the engine covers will hang a little over the inside of the transom. If someone were to sit at the helm while you were there (with motors off!) and turned the wheel back and forth, you should not be able to put your full fist between the transom and the bottom of the engin cover. If it's raised up much more than that, it's too high.

I dont have any shim on my rig. It's mounted to the boat at attatched at the lowest setting.

posted 01-21-2008 09:39 AM ET (US)            

I'm thinking about your payload. You said that you carry 10 scuba tanks. I would estimate that they are at least 40 lbs. each when full, that's about 400 lbs.) You also said: "We carry diving equipment, 2 big ice chests with ice, full water, full gas, sodas,beer and luggage etc... When I mean fully loaded is fully loaded..... . We even sometimes take gas in drums," How many gallons are you talking about in these "gas drums"?

This is quite a lot of weight. You may be carrying too much.

Where are you carrying the scuba tanks? You may want to try to balance your load. Have you seen those racks that attatch to the side of bow rails for holding fenders(or boat bumpers)? You way want to try to rig up some type of rack system to hold 5 scuba tanks on either side of the bow, inside the rails. In doing so, you are now placing about 400 lbs of wieght forward and most importantly "off the stern". I wouldnt put them all the way forward as they would obstruct your vision. If I were to guess, you are probably storing the 10 scuba tanks on the aft deck of the boat, along with the coolers.

Also, when loading your boat, try storing some of the heavier gear (for example weight belts for scuba diving) in the forward storage compartments in the cabin. Make sure the weights are wrapped in a towel, in case you encounter heavy seas. Anything that you can do to swap some of the weight from the stern of the boat towards the bow will help out a little in enabling the boat to get up on plane better.

Obviously, I am not trying to tell you to overload the bow area so that you are "bow heavy". I am just suggesting that you attempt to shift some of your weight towards the bow.

posted 01-21-2008 12:57 PM ET (US)            

I sent you and e-mail with photos showing how my outboards are mounted in my 285 Conquest. I hope that they help. Check your email.

posted 01-23-2008 01:13 PM ET (US)            

You mention up there ^^^ that you are hitting 6000 rpms at WOT with a little engine up trim. Then you mention that you load the boat up with several people and dive gear. Is that 6000 rpms reading with the heavy load or with just(lighter)you in the boat?

The reason I ask is that is a huge difference in weight. I can almost guarantee you that if the 6000rpms is loaded heavy, your boat would be way way under-propped when its light(no divers or gear). If your typical use is a "heavy condition" then you need to prop it considering that.

Not doubting what any other posters have mentioned, but I would lean towards the Merc Rev 4 or the Powertech OFS 4-bladed props. The Powertechs have a larger 15-1/2 diameter and may be better suited for your application. I would also stay away from porting the prop. In my experience, porting props on large heavy boats can lead to the boat basically stalling while coming onto plane........that is the point when the load on the propeller is the greatest. I could be wrong(wouldn't be the first time!) In my experience porting has worked well on smaller lighter rigs with a lot of horsepower. Bass boats are a good example of this. Or with aggressive style prop blades too.

Its hard to recommend a pitch with out knowing how the boat was loaded at your 6000 rpm reading.

Andy

posted 01-28-2008 10:56 PM ET (US)            

with the rev4 prop, same characteristics +/-8-10 SEG, 6000/6100 RPM=38.4 KNOTS, AT 4800 RPM=28.8 KNOTS AT 25 GPH.

AS YOU MAY NOTE IT DID IMPROVE SIGNIFICANTLY, I will try lowering one hole the engines to see if it mantains the actual conditions and be able to solve the ventilation issue.

I took some pictures of the actual rig, Is someone interested in comment them, send me your mails

posted 01-29-2008 08:26 AM ET (US)            

That's great news. Ain't it great when the guys on C.W. can come together and solve a problem.

I have the same set up that you have(except I have 225 4-strokes, not 250's) and I do feel that the Rev 4's that you switched to are the best props for your(our)particular rig.

posted 01-29-2008 11:25 AM ET (US)            

While you only gained 1 MPH in top speed, the much more significant improvement was your time to plane which has improved about 40 percent.

But what really caught my eye was the fuel economy. You have gone form 1.19 MPG at 31 MPH to 1.32 MPG at 33 MPH.