Tag Archives: performance

Friday 13th – unlucky for us, and performance data

Lady Luck

Took Befur out for a tour of the lake yesterday, enjoying a day of early autumn sunshine. Conscious that it was a fated day, I was expecting some drama!

Lou managed to (very narrowly) avoid a dunking while we were boarding, so I thought we might of escaped. However, bad planning on my part resulted in us getting blown onto a jetty on the lake, which was (unbeknown to us) fitted with large bolt ends projecting out to catch people in exactly our predicament – so more filling, sanding and re-painting required over the winter to repair a pair of gouges in the hull – bugger!

Performance Testing

One of my objectives for the trip, was to collect some performance data, and the map below (click the link and it should open in google maps) shows the route and the waypoints with speed, direction etc. (clicking on these will give performance data for each bit of the trip).

https://www.google.com/maps/d/u/0/edit?hl=en&hl=en&mid=1qv-Q4JREXMB5lKKMXQmANtZhy-Hxu3DD&ll=54.607108645724125%2C-2.8355938095091915&z=16

The net of this experimentation produced data on two “stable modes” of operation.  All of this at a boiler pressure cycling between 185 psi and 225 psi.

For the record we are now operating with a gear-up ratio from engine to propeller of 1.45:1 and a 21″ x 19″, 3 bladed, left hand prop.

At “cruising speed”

At this speed we are operating with a HP pressure of 60-70 psi, and an LP pressure of around 16 psi and a vacuum of about 10-inches. The engine is turning at between 175 rpm and 125 rpm (when alternator is charging). The map tells us we are moving at about 3 mph (2.6 knts), it was running into fairly light winds, so this data seems realistic.

At “flank speed”

This is about as fast as I feel happy running the plant, and is resulting in the engine slightly outrunning the boiler with a sustained boiler pressure of about 170 psi.. HP pressure is 135 psi, LP pressure 28 psi, vacuum of 14-inches. The engine is turning at 300 rpm and the log tells us she is making between 6.5 to 7.2 mph.

…so with a computed hull speed of just under 8 mph we still have a way to go on the performance stakes.

Those with better maths than I might be able to turn this into some meaningful performance data for the engine hull.

We also had the time to check the depth sounder and it certainly seems to work, with the audible alarm providing some confidence for the helms-person when we are running out of water!

…onwards, it will be “dragging out” time in the next few weeks, and then we can fix the outstanding mechanical issues, ifx the knocks and bangs, fit the mast and figure out how to stop the water getting into the cabin roof!