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ContinuousWave: Post-Classic Whalers
To trim tab or not to tab
|Author||Topic: To trim tab or not to tab|
posted 07-14-2005 01:33 AM ET (US)
05 nantuckett with 135 optio I plan on using this mostly in the ocean would trim tabs help stabalize or not?
posted 07-14-2005 03:44 AM ET (US)
Yes, it is on my get list.
posted 07-14-2005 08:58 AM ET (US)
Don't leave home without them. Here's a terrific overview of what tabs can do for your boat.
"This written by Tom McGow of Bennett Marine, www.bennetttrimtabs.com 954 427 1400, Deerfield Beach, Fl.
Trim Tabs and motor trim are best used together to get the maximum performance:
It is a common misconception that if a boat has power trim on the outboard or outdrive it does not need trim tabs. Power trim can be used to adjust the boat's attitude, but it is highly inefficient. A propeller is designed to force the boat forward. When trimming the boat with the prop, the prop must not only push the boat forward but raise the stern as well. In this situation, prop slippage is greatly increased thereby wasting R.P.M.'s. Power trim cannot correct listing, and is ineffective at slower speeds. Trim Tabs, in combination with power trim, enable both the hull and prop to be trimmed independently. The trim tabs trim the hull, while the power trim adjusts the prop. The result is optimum performance and efficiency not attainable by the use of power trim alone.
To acheive maximum performance, first adjust the trim tabs to achieve the desired running attitude. Next, use the power trim to position the propeller thrust parallel to the water flow. If necessary, re-adjust the trim tabs to fine tune the attitude. By observing the boat’s speed and engine RPMs the best combination of trim tabs and power trim will be apparent. Trim tab angle indicators and a power trim angle indicator are particularly useful in duplicating effective settings.
The key to getting the best out of Trim Tabs is experimenting with them since all boats are different. Use them in short bursts and let the boat settle down between corrections. Below you will find a little Trim Tabs 101 that should help you get started.
Getting and Staying Trimmed
All boats assume different fore to aft attitudes at different throttle settings and vary in sensitivity to lateral weight distribution.
A boat’s optimum running attitude is determined by the operator. While some people may define optimum running attitude as the highest possible speed for a given amount of engine RPMs, others desire the best possible fuel economy, yet others may be trimming the boat to get just the right mix of speed and wake (such as for waterskiing.)
A good way to determine a boats optimum running angle (see side bar Optimum Running Attitude) is to run the boat lightly loaded at full speed in calm water. During this test observe the boat’s bow in relation to the horizon. Most boats run at or near their optimum attitude under these conditions. This should give you a feel for the appearance of the wake and bow spray when running at an efficient attitude. Note that not all boats will achieve their optimum running attitude under these conditions. Some boats will benefit from extra lift even when running at their maximum throttle settings. If you feel the boat will benefit from added bow down trim when running at speed start with the trim tabs fully up and deflect the trim tabs in short bursts. Be alert to changes in the boats handling, as you bring the bow down. Observe any changes in RPMs and/or speed. Adjust power trim if applicable.
Indications of Running Untrimmed
Indications of Running Trimmed
One Step at a Time
Getting the Most from Power Trim
Trimming to Sea Conditions
As previously mentioned the normal control setup for trim tabs operates in relation to the desired changes in trim and not the actual movement of the tabs. Therefore, do not think about what the tabs are doing, but rather on the control and what you want the boat to do. As above, make the corrections in bursts and allow the boat to settle to the new settings. You may find it easier to correct the boat’s fore and aft attitude before you correct the athwartship trim.
Correction of Porpoising
posted 07-14-2005 09:47 AM ET (US)
Trim tabs have almost no effect on stability. The hull form and weight distribution are the principal influences on stability.
posted 07-14-2005 12:30 PM ET (US)
I would imagine that a Nantucket is a large enough to benefit from trim tabs. Just by going from half a tank of fuel to a full tank and putting a couple of average sized fishing buddies in the stern seats would add around 600lbs of extra weight making you stern heavy and probably cause you run too bow high in most conditions except flat out on smooth water. The tabs would allow you to overcome the added weight and make you run at a proper attitude at slower speeds which is necessary when the conditions get rough. Tabs will also help you run straight and level just in case one of those fishing buddies in your stern seat is substantially heavier than the other one.
I couldn’t even run my boat without without tabs. Two passengers, the extra weight of a full vs. half a tank of gas, and the extra weight of a twin engine is around 1300 lbs.
posted 07-14-2005 12:36 PM ET (US)
That's a great excerpt Tom. Thanks for that.
posted 07-14-2005 12:42 PM ET (US)
Properly used trim tabs are a very valuable tool for offshore work.
posted 07-14-2005 12:46 PM ET (US)
BTW Jim, trim tabs can have an effect on the stability of a properly designed boat by compensating for an uneven load while underway.
posted 07-14-2005 01:48 PM ET (US)
I would like to have tabs to compensate for load variations and to help trim the bow down at very low speeds.
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