Space in boats is precious. It is also sometimes difficult to visualize the spaces in a boat. Building right angles inside of a curved hull makes for some little cubbies and strange voids. One of those spaces in our boat yielded a surprise. My guy unscrewed the plywood under a low shelf and he found these:
O-o-o-oh, feels like Christmas morning!
They looked pretty good, but they didn’t match the propellers that are currently on the boat.
Those markings mean that the props on the boat are 28 inches in diameter with a pitch of 24 inches (28x24). The spare set are 26x22. Sizing propellers for a boat is a mixture of math, science, art, and experimentation. Figuring out the best fit is way out of my grasp. Would the spare set of props work for our boat? We went to a professional propeller shop to ask.
Rod Bray at Union Machine asked for some information. He wanted to know the size of the propellers that we had on the boat, the engine rpm’s at full throttle, and the marine gear (transmission) ratio. We took the boat out and ran the rpm’s up. Things didn’t feel good. I stayed at the helm and my mechanically inclined sweetheart went down to the engine room. He brought the rpm’s up a little bit more and things were not happy at all. We are overwheeled - the propellers that are currently on the boat are too big. The engines would not come up to their rated speed. When the engines are trying to swing oversized propellers then they are working too hard and burning too much fuel.
Rod Bray did some of his prop-wizard math, and said that the spare set of props is closer to what we need. I foolishly questioned whether the spares needed to be trued up. Well, they looked okay to me! I just needed to polish them and we could put them on. Wrong!
There was a slight bend in one of the blades, and Rod’s trained eye picked it up almost immediately. After measuring he also found that one of the blades was way out of alignment. If we had put those propellers on in that condition then it would cause terrible vibrations and possibly do damage to the boat. This has been my lesson in the value of a good prop shop.
Union Machine Shop fixed up the propellers. They also tapped the props and made a puller for them. The next time this set of props needs to come off of the boat that puller will make it a much easier process.
The props were shipped back to us by barge. When the wood box came in at the freight company it was like Christmas all over again. We opened the box and…
M-m-m-m, shiny-pre-eddy! Prop Art! So pretty that it is a shame to put them into the ocean. I want to hang them on the wall as art! I want to make them into a centerpiece on a big table. I want to install them as a gently turning hanging sculpture. Those possibilities are not to be, though. The propellers will be underwater art.
Properly sized propellers will be much better for the boat. The engines should run more efficiently and last longer. The boat should handle better, too.
In a few weeks we will have the boat hauled out to clean and paint the bottom. We’ll also put those shiny propellers on, and I’ll let you know how that works out.
May your day be propelled by art and motion,
See how the propellers went on - Installing the Propellers