I am considering changing from a two-bladed to a three-bladed prop on my I 28 equipped with the original 13 hp MD7A Volvo diesel. I am having a devil of a time determining the gear ratio and prop dimensions for this boat (I believe the prop dimensions are on the prop but it is in a shop some distance from here). My best guess at these dimensions for my present two-bladed prop and this engine are as follows: 12 X 6 X 3/4" X LH. I believe that the shaft reduction ratio is 1.91:1. The engine maximum rpm (for 13 hp output) I believe to be 2,600 rpm. Can anybody confirm or correct these figures?
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These are the numbers from a diesel web site
for a boat of 7500 lbs and a 22 foot WL Gear Ratio Shaft RPM Dia. Pitch 1.6-----------1750----11----7 1.8-----------1556----12----8 2-------------1400----13----9 2.2-----------1273----14----9 2.4-----------1167----14---10 2.6-----------1077----15---11 2.8 1000 16 12 3 933 16 13 No other suggestions using practical gear ratios. I tried to place the numbers below the words.
for a boat of 7500 lbs and a 22 foot WL Gear Ratio Shaft RPM Dia. Pitch 1.6-----------1750----11----7 1.8-----------1556----12----8 2-------------1400----13----9 2.2-----------1273----14----9 2.4-----------1167----14---10 2.6-----------1077----15---11 2.8 1000 16 12 3 933 16 13 No other suggestions using practical gear ratios. I tried to place the numbers below the words.
Numbers stamped on this propeller???
I have just heard back from the marina where the boat is being painted and they have looked at the lettering stamped on the propeller hub. They said that the letters are very hard to read but look something like: 12L1114. They said that these marks could also be 12L1J14 and that the first '1' could also be an 'I.' I wonder if the last part of this stamp is '3/4' for the shaft diameter, the first three marks are for 12" and left hand pitch and the rest of the marks have to do with the pitch. If so, the pitch does not seem to agree with the 6" which I presume is correct for this engine and boat (from the specificationf of other boats of this vintage which had very similar size and the same engine). Again, does anybody out there with an I 28 and the old MD7A engine know their propeller and reduction gear ratios? I presume that both the reduction gear and engine are stock and that this boat was constructed in 1978. I also am aware that by the early 1980's Islander Yachts were using Yanmar diesels instead of Volvos which, altough of similar size and horsepower, had right-hand propellers.
I have just heard back from the marina where the boat is being painted and they have looked at the lettering stamped on the propeller hub. They said that the letters are very hard to read but look something like: 12L1114. They said that these marks could also be 12L1J14 and that the first '1' could also be an 'I.' I wonder if the last part of this stamp is '3/4' for the shaft diameter, the first three marks are for 12" and left hand pitch and the rest of the marks have to do with the pitch. If so, the pitch does not seem to agree with the 6" which I presume is correct for this engine and boat (from the specificationf of other boats of this vintage which had very similar size and the same engine). Again, does anybody out there with an I 28 and the old MD7A engine know their propeller and reduction gear ratios? I presume that both the reduction gear and engine are stock and that this boat was constructed in 1978. I also am aware that by the early 1980's Islander Yachts were using Yanmar diesels instead of Volvos which, altough of similar size and horsepower, had right-hand propellers.
Propeller problem solved...
After cleaning up the propeller and taking it to a prop shop, I found that it was actually a 12 X 14 X 3/4 LH prop which is apparently typical for the MD7A Volvo engine and its associated 1.91:1 reduction gear. Knowing this, I purchased a 12 X 10 X 3/4 LH Campbell Sailer 3-bladed prop.
After cleaning up the propeller and taking it to a prop shop, I found that it was actually a 12 X 14 X 3/4 LH prop which is apparently typical for the MD7A Volvo engine and its associated 1.91:1 reduction gear. Knowing this, I purchased a 12 X 10 X 3/4 LH Campbell Sailer 3-bladed prop.
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