Inboard propeller shaft angle and shaft layout diagrams

At an early stage in your build, it would be wise to create a shaft layout diagram to see which engine/trans can be fitted in the design that you've chosen.  If you're stretching the hull in order to install a longer, more powerful engine, a diagram will be crucial in determining how much extra length will be required to fit the engine and transmission and calculate the installation's propeller shaft angle.

Before you get too far into your project, you'll need a few tools :

• Engine selection, transmission gearing, propeller selection and shaft layout diagrams are covered in great detail in the book Inboard Motor Installations by Glen L. Witt & Ken Hankinson.
  
• Chapter 11 - Shaft angles & layouts is available online : Inboard Motor Installation Chapter 11 : Shaft Angles & Layouts (WebLetter 12)
  
• Dave Lott has taken the time to document the shaft layout and shaft hole boring process : Riviera Shaft Hole Boring by Dave Lott, Glen-L Riviera builder (MS Word document)
  

The following screenshot is a digital version of Dave's shaft layout method.  We've expanded the spreadsheet to compute shaft angles for four engine displacements and two strut drops for each engine.  It looks rather confusing but it saves having to rerun the spreadsheet with other data.

Notes

The first table contains engine dimensions and shaft layout data from previously scaled shaft layout diagrams.  The four engines are installed at the same shaft angle.  The second table calculates the shaft angles for each engine installed at a fixed distance from the transom.

Analysis

If you're installing an engine in a tight space and wish to minimize the shaft angle, scan the Shaft Angle column to find the best fit.  In this example, a flywheel-forward installation is the best fit.  It's followed by the 4.3 V6. The other angles are too steep if your goal is to stay below the 15 degree maximum.  Stretching the hull and running the numbers again will flatten out the shaft angle.

You'll find more info and calculators on our website's Transmission Page. Here's a direct link to the shaft layout section : Shaft Angles & Layouts - Drilling the Shaft Hole

Building the Glen-L Hot Rod : www.boats.chelseacoachworks.com      Revised 05-APR-2013