1991 21 WALKAROUND Slow to Plane with 225-HP

Optimizing the performance of Boston Whaler boats
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Joined: Mon Aug 07, 2017 7:06 pm

1991 21 WALKAROUND Slow to Plane with 225-HP

Postby kaneroberts » Mon Aug 07, 2017 7:14 pm

I just bought a 1991 21 WALKAROUND with a 2003 HONDA 225 with a 14.75 x 18-pitch three-blade propeller. The boat is slow to get to plane, but once it gets to plane it is super fast.

What can I do to get the boat to plane quicker?

I fish out of San Diego and don't need a huge top end of speed because of rough seas, so 25 to 30 nautical-miles-per-hour is the maximum [usable boat speed]. I also want good fuel consumption because we make long runs to fishing spots.

What do you suggest?

I just bought the boat so I don't have much to compare to and don't know if this changed throughout thehistory of boat. Thanks for the help.

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Location: Michigan, Lower Peninsula

Re: 1991 21 WALKAROUND Slow to Plane with 225-HP

Postby jimh » Mon Aug 07, 2017 11:00 pm

You need to monitor engine speed with an accurate tachometer to keep full-throttle engine speed confined to the recommended maximum engine speed range. Look up the data for your engine. Make some runs with the present propeller and record boat speed and engine speed in the planing region, all the way to maximum throttle and maximum boat and engine speeds. Give us some data in a table of engine speeds and boat speeds.

Also give us some details on the propeller on there now. Who made it? Is it using a universal hub system with field-replaceable inserts?

Give us data on the gear ratio and recommended engine speed range at full throttle.

To improve acceleration onto plane, reduce the propeller pitch. Try moving to a 17-pitch. Changing to a four-blade propeller may help the engine get the boat on plane faster. A propeller with more diameter may help, too. I can't offer a particular propeller to test--see what you can find in the way of loaner propellers from a dealer who participates with a propeller manufacturer and has some test propellers available for sea trials.

If the engine is an older HONDA BF225 it may not have a really wide power curve; it may not have much horsepower or torque at low engine speeds. Sometimes this can be overcome by using a propeller with a hub that has vents. The vents can be opened up to let some exhaust gas escape, and the exhaust gas will create airy water around the propeller. This makes the propeller slip, but allows the engine to accelerate. It is somewhat like a rubber-band drive--it stretches the effective propeller pitch to be lower during acceleration, and then when planing speed is reached the Venturi effect of the boat motion draws all the exhaust out the hub, so the open vents stop leaking any exhaust gas into the blades. Propeller then acts like its full pitch.

Also, get any weight out of the stern of the boat. I have been on a 21 WALKAROUND that was struggling to get on plane with extra weight in the stern--me sitting there. The hull seemed to have a lot of bow rise, and then, slowly, boat speed would build up and the bow would come down. I think weight in the stern aggravates that situation. Maybe move some gear out of the stern, or even move the batteries out of the stern.

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Joined: Tue Oct 20, 2015 8:46 am

Re: 1991 21 WALKAROUND Slow to Plane with 225-HP

Postby Acseatsri » Thu Aug 10, 2017 6:22 pm

That motor is over 200 lbs heavier than the 175 hp 2-smoke that most of these boats came rigged with (about 600 lbs for the Honda vs 380 or so for the 175 2-smoke). I had a Honda 250 on mine and ended up moving the batteries to the bow before finally buying a 23' walkaround with 2 old 150 2-smokes and swapping the 250 for one of the old 150's from the 23 and selling the 21. The 21' is an ass-heavy boat to begin with, plus the steep angle of the bow means that the wetted area of the hull is shorter than most boats this size. With the lighter 150 hp engine, it's a great boat and rides really well, top speed is about 37 mph with the 150 vs almost 50 mph with the 250. In my opinion, the motor on this hull shouldn't be heavier than 400 lbs or so.

Another thing that will help is plugging the fish wells. With that heavy motor and a few people sitting in the cockpit, it doesn't take much to overflow the fish wells into the bilge. From my experiences.

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Joined: Fri Oct 16, 2015 7:06 am

Re: 1991 21 WALKAROUND Slow to Plane with 225-HP

Postby rtk » Fri Aug 11, 2017 8:04 am

Does the boat have trim tabs? They would certainly help with planing and all around boat handling, I found them to be necessary on the 1996 21 Outrage I had,