6. Measure Transom Angle

Measure Transom Angle Introduction

Seakeeper Ride Controllers must be mounted as close to parallel with the running surface of the hull as possible, as explained in Section 5. This portion of the installation is to measure the angle at the chosen locations. The Wedge Pack Assembly (Items 4, 5, 6, 7, and 8 in Figure 5) allows for the adjustment of the Controllers to the boat’s transom angle. The figure below illustrates the differences in the angle between the aft end of the running surface and the transom (A) and the resulting effects on Wedge Pack selection (B). The top two images show correct angle adjustments. The bottom two images show incorrect angle adjustments.

Figure 20 – Different Transom Angles and the Effects on Seakeeper Ride’s Geometry

For optimal performance, the Seal Plate must be completely flush with the aft end of the running surface of the boat, which will eliminate angle C in the figure above. The Seal Plate can angle upward up to 2 degrees with a negligible effect on system performance. If the Seal Plate angles upward more than 2 degrees, or if the Seal Plate angles downward at all, a significant negative impact on the performance of the system will result.

Figure 21 – Seal Plate Acceptable Angle

6.1. Measurement Steps

  1. Using the selected Controller locations from Section 5, measure the angle with a digital protractor from the running surface to the transom, perpendicular to the deadrise. See the figure below for an example of the measurement on the port Controller, outboard location.
  2. Measure the inboard and outboard ends of the port Controller area and use the larger angle in the following Sections. Round up to the nearest degree.
  3. Measure inboard and outboard ends of the starboard Controller area and use the larger angle in the following Sections. Round up to the nearest degree. Note: It is possible to find different angles between port and starboard side of the hull.
Figure 22 – Measuring Port Side, Outboard, Transom Angle
  1. Determine the number of wedges required for each Controller’s Wedge Pack using the transom angle measured in previous sections and Table 2 – Transom Angle and Wedge Plates.

The transom and Wedge angles indicated in the Table 2 are the maximum range of the product. If the boat’s transom angle is outside the range of Table 2, do not add or remove more wedges to accommodate the different angle. Contact Seakeeper to determine the best course of action.

Table 2 – Wedge Plates Based on Transom Angle

Wedge Plates
Measured Angle3 Degree4 Degree5 DegreeTop Bolt Length
112°150 mm
111°150 mm
110°150 mm
109°260 mm
108°1160 mm
107°1160 mm
106°1160 mm
105°260 mm
104°1260 mm
103°11160 mm
102°1260 mm
101°1260 mm
100°21160 mm
99°2260 mm
98°11260 mm
97°2260 mm

6.2. Hulls with Unique Stern Features

For many planing hulls, the aft portion of the running surface is straight, however, there can be exceptions where there is a curvature, angle, or twist just forward of the transom. This may be referred to as a stern wedge, hook, or rocker. These types of features are generally added the hull to improve handling characteristics or induce a constant trim, adding a bow down moment during normal running conditions.

Be sure to use a 3-ft (0.9 m) straight edge along the hull bottom when evaluating the transom angles to obtain a correct assessment of the running surface.

If the Seal Plate were to be installed following the same angle as a stern wedge, it would create a permanent additional upward force in the aft of the boat, and the bow would be pushed down irreversibly. This incorrect assessment for installation is demonstrated below.

Figure 23 – Incorrect Assessment of Running Surface

Measure the angle of the transom over a greater length of the running surface up to 3-ft (0.9 m) to ensure the proper angle.

Figure 24 – Correct Assessment of Running Surface with an Extra Long Straight Edge