Removed Old Volvo MD 21A

Took the old engine out using my homemade hoist.

Engine and Propeller Sizing

After reading Nigel Calder's Engine and Propeller section in Chapter Five of his book Nigel Calder's Cruising Handbook, I plugged in his math into a Microsoft XL spreadsheet to determine engine and propeller sizing. Below is the spreadsheet with the Hallberg Rassy Rasmus specs plugged in. Use at your own risk.

The shaft HP is what is needed to drive the boat at hull speed. However, there are losses of power in the system that need to be adjusted for such as alternators, engine driven refrigeration, and mechanical losses. Nigel divides the shaft hp number, in this case 31.89 hp by .95 and then adds around 3 hp for every alternator added of 100 amps. So if you plan to add a 100 amp alternator the horse power needed to drive the Rasmus rises from 31.89 hp to 37 hp including mech. losses. Without the 100 amp aternator you would need a 34 hp eninge. Looking at these calculations the minimum hp to drive the Rasmus is a 34 hp engine. I have read of Rasmus owners being very happy with 30 hp engine in their boats. Also have heard of owners being happy with their new 43 hp engines in them. In propeller sizing, I have plugged in the specs for a Westerbeke 35D engine with a 2.47/1 reduction gear. This is the engine I am seriously considering along with the Beta Marine 38. The Rasmus has an aperature of 22 inches for the propeller to spin within and it is recommended to have a 10 to 15 percent clearance between tips of propeller blades and boat. Using a 10 percent clearance factor, the maximum propeller diameter is 17.6 inches. Hull speed and shaft rotation in rpm determine propeller pitch and shaft hp determines propeller diameter. You can change engine size in hp, transmission gearing, and engine rpm's to adjust for propeller diameter and pitch. With a 31 hp engine rated at 3000 rpm with a 2.47/1 reduction gear, the recommended propeller diameter is 17.31 inches with a 13.58 pitch.Click here for pdf file on engine and propeller fit


I keep trying to convince myself to go engineless with this motorsailer. Crazy huh? And now I see all the millions of gallons of oil polluting our beautiful gulf coast, it really gets me motivated to make it work, that is, without an engine. The BP spill will reach the Gulf Coast National Seashore's barrier islands, a place that I have explored in my wooden dory. It is a magical place that I have grown to love. My first trip out to the islands, Darryl and I left out of the Hard Rock Casino boat launch in Biloxi headed for East Ship Island. The wind was blowing hard. I was tempted to abort the trip. A local walked up looking at our unusual boat and asked where we were headed. We told him we were headed to Ship Island. He said, "in that, today, your going to die". Well we didn't but it literally scared the pee out of me. We motored thru 4-6 foot chop for 4 hours with our trusty nissan 5 hp motor. We had to bail out the boat several times along the way. We didn't see another boat that day, just us and the bay. When we reached East Ship Island, it felt special. We were on this very small, desolate spit of land. Just us. It was raw and beautiful and I felt we had accomplished something that day. And man was I glad to be standing on land after that exciting ride. I am glad I exlored those isands. Who knows their fate at this point. Gulf Shore Barrier Islands