JUST 3 TO 4 MPH MORE

QUESTION: I have a 1998 28 Skater with 2005 Mercury 250XS engines that I bought at the beginning of the summer. After experiencing problems with the fuel tanks melting because of the ethanol dissolving the resin in the tanks, now my “real” problem is not being able to break the 100-mph mark. The boat can get to 97 or 98 mph at 6,200 rpm. I’m turning Mercury 14 1/2" x 32" props outward, with 1.62:1 gear ratios in Sport Master cases. I have 25 psi water pressure and the engines are bolted directly to the transom.

Will jack plates or different props help? If so, will the plates change the handling characteristics? The prop shafts are about an inch above the bottom of the boat. What about switching to four-blade props?

Another problem is that one of the motors will go up to about 6,000 rpm and then start holding back to 4,500 to 4,800 rpm without the electric fuel pumps being turned on, which were already installed in the boat when I got it. There were different engines on it at one time. If I shut off the engine for about 30 seconds, it’s good for about 2 minutes before it starts happening again. The engine runs OK with the fuel pumps on. Could the fuel-pump diaphragms in the engines be bad? I’m just looking for another 3 to 4 mph if you think it’s possible. The boat is used in Sag Harbor in New York.

ANSWER: Your Skater 28 bottom is pretty much the same as current 28 Skater outboard catamarans. So what works on their new boats will probably work on yours. When your boat was built 10 years ago, ethanol and other similar fuel additives were not on the radar screen. There are many brands of boats out there that are having problems with fiberglass fuel tanks.

The good news is that Douglas Marine has developed a fix for your tanks. The first thing you should do is contact them and find out what you need to do. There is probably a facility close to you that has been trained on installing tank liners in your boat.

Your boat was apparently originally equipped with Mercury 2.5 outboard motors. They required the use of the electric fuel pumps. I suspect that your fuel starvation problem is not because of something being wrong with your newer engines. I believe that you still have a problem with fuel delivery because of debris from the fuel tanks. It sounds like whatever is causing the flow restriction builds up in the system, causing a partial and increasing flow restriction. When you shut off the motor, the debris falls away momentarily, but then goes back into position with increased fuel flow.

Most fuel pumps have an internal screen. Disassemble the pump and make sure the screen is not clogged with debris. Also, you will need to change your water separator filters on a regular basis until the system is clean again. There may be a flow restriction merely because the fuel pumps are in line and your engine fuel systems are drawing through them. I cannot say for sure without knowing how they are plumbed. The bottom line is that your tanks and fuel system problems must be correctly addressed before you go about taking steps to increase speed.

If your boat was originally equipped with Mercury 2.5 outboards, it is likely that the length of your newer engines is not the same. Unless the new engines were installed at a height to compensate for the difference, your prop shafts are probably lower than when the boat was first built.

Peter Hledin, the owner of Douglas Marine, recommends installing jack plates on the boat. This will enable you to make the finite adjustments necessary to maximize your performance. When dealing with high-performance outboards on a catamaran, engine height adjustments as small as 1/8 inch can make a huge difference. Douglas Marine has been installing a heavy-duty competition jack plate assembly made by Cook Machine. The particular unit they are using has a short stroke and only results in about a 4-inch setback.

Your current water pressure of 25 psi is adequate. If you find that raising the engine to achieve maximum performance results in low water pressure, the bottom of the boat can be modified slightly to address the problem. This is done by grinding a slot about 1-inch wide in the bottom running surface directly in front of the gear case that is about 1/8-inch deep at the transom and diminishing to nothing about 8 or so inches forward. This slot will help direct water to the water inlets on the gear case when the jack plate is in a higher position.

Once you get your fuel system sorted out and the engines installed on the jack plates, it is then time to start trying different propellers. I would start by contacting other people who have a similar boat with similar power to see what is working for them. Ultimately, you will just have to start bolting propellers on and experiment when you are looking for that last 3 or 4 mph. I think you will be able to achieve your goal.

LOVES OUTBOARDS

QUESTION: I have a 1978 Cigarette 35 Mistress hull with no engines or rigging. What is your opinion on instead of installing the customary big-blocks in my boat, adding an outboard engine bracket/swim platform and going with 300-hp, four-stroke outboards?

I realize that I will be making a compromise when it comes to horsepower and speed, but I have better luck with outboards. Do you think this setup will function? What is your opinion on modifying a classic?

ANSWER: There is no question that the boat will probably work similar to some of the larger nonstepped-bottom center-consoles. A Midnight Express is one of the higher-end outboard-powered center-console boats and has many similar hull characteristics when compared to your Cigarette. One of the main things you need to consider is the cost of your project and how much the boat will ultimately be worth.

If your boat has no engines and drives right now, it is possible that you could put it into nice running condition with some late-model takeout Bravo XR packages with 500EFIs or 525EFIs for between $30,000 to $70,000, depending on what deals are available to you.

A standard inboard/stern drive installation will enable you to use the original engine hatch and cockpit layout.

This type of inboard power is what would normally be expected in your boat. You would never have to explain yourself to potential buyers with the Bravo XR packages and the boat would have reasonable resale value.

If you choose the outboard program, you should plan on installing a minimum of three of them. Some boats in your size and weight range run four big Verados. I think they would install five if they would fit (Midnight Express actually told me that once).

It is easy to see that if you intend to buy three or four of these late-model, four-stroke outboards, your expense will be much higher than keeping the boat as it was originally designed with inboards and stern drives.

You also will have to choose what to do with the large space that is now the engine compartment. It would make sense to move the firewall and rear bench seat back and enlarge the cockpit area. You could leave a small area accessible through redesigned hatches for rigging and batteries.

One thing that I am not sure of is how the balance of the boat will be with all that weight hanging 3 to 4 feet behind the transom. I am guessing that the bow will go into the air easily when hitting waves unless some weight is added up front. If the boat is as heavy as a "tank" now, the weight placement will not be as critical.

Be aware that the big outboards use a fair amount of fuel when installed on heavy boats that are capable of using all of their power.

Depending on how you operate your boat, it is possible to use more fuel at cruising speed with a few big Verados than you would with a pair of fuel-injected 502s.

—Need some guidance from Bob Teague, Powerboat's lead test driver and owner of Teague Custom Marine? To send him an email click here.

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