Monitor Manual
3 Installing the Monitor
3.2.4 Importance of the Boat's Wake
The level indicated above is a rule of thumb, which is subject to much variation. The proper location of the vane gear, up or down, should be determined by the dynamic waterline which is created when the boat is moving at different speeds on different points of sail.
Each boat is different, and its owner best knows its characteristics. However, with the experience from years of installations and proper records we feel that our recommendation and installation drawing in general can be considered correct if proper measurements have been given to us in the first place. However, here are some additional guidelines to be used in determining proper mounting height.
The paddle at the end of the servo-pendulum is the power source of the vane gear. As long as a part of the paddle is immersed in the wake behind the boat, the vane gear will operate as designed. It is very unlikely that the servo-paddle will lift out of the water occasionally, but it could possibly happen to a yacht with very long overhangs in choppy seas or a boat with an extremely wide transom. This will not seriously interfere with the efficiency of the gear. However, if the paddle remains out of the water for long periods, the performance of the vane will be affected. Nothing is gained by mounting the vane gear so low that not only the paddle but also the pendulum shaft is covered by the wake. The strains on the welds and mountings multiply without any improvement in the functioning of the gear.
From this it follows that the MONITOR should be mounted so that the water paddle is always immersed to some degree yet the pendulum shaft and hinge are immersed as little and as seldom as possible.
Some boats have very different waterlines at the stern when they are still versus when they are moving fast. Yachts with long overhangs generally have water all the way up under the transom when sailing downwind at cruising speed. The wake can result in the water being much higher on the transom than when the boat is still or moving slowly. Double-ended hulls tend to squat, especially going downwind, and, if the stern is fine, with little buoyancy, the wake can sometimes climb very high. In these cases, the vane gear must be mounted as high as possible while still keeping the paddle immersed, to some degree, at slower speeds and on different points of sail. This is especially important if the boat is large and fast or uses an extra long pendulum shaft, which also increases the loads on the gear.
IN SUMMARY: You are pretty safe following the factory installation drawing that we have provided. If it is a popular boat we probably have had lots of sister ships with MONITOR and the drawing is based on plenty of feedback.
Six inches of the paddle out of the water, on a stationary boat, fully loaded, at the dock, is correct in most cases. Sometimes it might be a good idea to observe the wake of the boat on different points of sail and in various conditions. This could be done, for example, by using a clearly marked yardstick to assess the level of the wake. If this level varies much, there will be times when the safety tube and even the pendulum shaft are immersed to some degree. There is no cause for panic as the MONITOR is built to withstand great loads. However, there is no point in increasing these loads unnecessarily, and we have found that the tendency is always to mount the vane gear too low rather than too high.
If in doubt, always mount the MONITOR HIGHER rather than lower unless you already have the maximum +6" or +8" safety tube. We rarely see the MONITOR mounted too high, but sometimes we see installations that are too low. If you mount the MONITOR too high, the paddle can be lowered by a longer safety tube, which we would supply. The longer tube gives your MONITOR more leverage, which yields more power.
There are too many variables to always sail with the perfect submersion of the water paddle at all times. Big crew in the cockpit or on the foredeck, upwind or down wind, full or empty fuel and water tanks, lots of supplies or no supplies are only a few factors that will influence the waterline. Through the years we have seen a few severe mounting mistakes but it really does not seem to matter. The reason for this whole discussion about the waterline is that we are simply trying to get the mounting as correct as possible for a variety of conditions.
Two more observations: All cruising boats seem to put more supplies and more weight on board than expected, and all boats seem to really squat under power.
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