#189 Sailboat Propulsion Issues!
Articles, Blog

#189 Sailboat Propulsion Issues!

January 14, 2020

for those of you who just following us
we had a brand new transmission installed with new control cables and a
new damper plate and when it came time to take out the boat and see how it
operates encountered a lot of difficulties this extreme loss of power wasn’t sure why that was so we began the
process of troubleshooting to figure it out the first thing we realized was that
the ratio of the new transmission which is the replacement for the old
transmission which has not made anymore because it’s an old boat from 1983 I
then also thought gee maybe there’s something fouling the propeller so the
next challenge was to see if we could take a look at the propeller without
diving into water that’s got alligators in it so we came up with the plan to put
a GoPro on the end of the stick it looks like not only is the propeller pretty
fouled which would make it understandable why even in Reverse where
the ratio is not as great we’ve lost some power in the forward where the
ratio is significantly different we really hardly have any power at all so
looks like we need to clean the hall and probably get a new propeller so I have
the following challenges number one how do I clean the hull and the propeller
that’s existing on there now without getting eaten by an alligator hey everybody how you doing
first want to thank all you guys for your comments and on one hand that’s
really great because it gives me lots to think about it can also be kind of
confusing because but I just see a theme and I think the best advice I’ve gotten
is for me to contact a propellor place and talk to them about you know the
situation so stay tuned and the end of the video you’ll see the decision that
I’ve made here’s a hint spoiler alert I’m getting the boat really well cleaned
the whole is gonna be clean and the propeller clean because I need to try
one more time to see if I can operate this boat more effectively with a
completely clean propeller and a clean bottom hull check it out and thanks for
watching the video and we’ll see how we get to the end of this process so we can
move forward and again appreciate all your guys input keep sending your
comments and sometimes it takes me a while to respond or to even get them
posted because things have been kind of hectic I don’t know about any of you but
it seems like this last month has been a bit chaotic I don’t know if you can
relate to that if things are going smooth for you but it’s just been kind
of a crazy month so I’m hoping that things are gonna shift into a little
more of a you know easy peaceful way so alright talk to you soon
how do I go about even finding out what is the proper propeller diameter and the
proper pitch size for my engine and for the weight of our vessel sounds like
there’s a lot more to research and learn so in the meantime I figured you know
doing the research on my computer I can do something practical time to finally
inspect my steering you so I made a list of some of the main
propeller makers and I called them up and told them the situation as far as
the horsepower of my engine the new ratio of my transmission the make and
model of the boat and all the different specs that they wanted to begin to get a
sense of what’s going on and what do I need to do my name is Kelsey West by
Mars industries about a propeller for your moody 34 ya with a 30 horse motor
you should be running a three blade anyway the 34 horse to place kind of a
waste all right I’m gonna have to set this up and run some numbers yeah I
calculate all it is a full hydrodynamic sizing dancy a question right okay oh
yeah from one point eight to two point one isn’t that big of a difference it’s
one inch difference in pitch it’s not that big a deal
what kind of thing is I’m saying is what you did do you may it may have been
overloading the engine I don’t know I would expect it was with a 1.8 to one
and a fifteen by twelve so that is a 3000 rpm engine wondering if in flat
water you’re able to get 3000 or no I never even needed to go I think the most
I ever had it was 2500 I understand that completely
I mean you can set it up however you want the engine is designed to run at
3,000 rpms okay the propeller should allow it to get there if it wasn’t
before you were overloading the engines and not doing what’s right for the
longevity of the engine right so you couldn’t I mean we can overload it if
you want I can tell you what the difference between the 15 by 12 at 1.8
and the 15 would be to get the same loading of the engines you had before
that doesn’t mean it’s right for the engine gotcha
well what propeller you think we would recommend for further I mean that should
load up the engine correctly to be a blunt Anana
the fifteen by twelve two blades should do the right thing for that engine well
I’m getting the whole clean on Tuesday morning really good and the propeller
making sure it’s clean down there right so maybe it maybe I’m losing some power
because it’s more foul than it thirty percent of the boat speed you know the
hottest holes covered in the profits covered you lose you know thirty percent
of what you had before just from growth right okay you’re lowering lanes in less
than you did before but you’re loading it more correctly we
okay well that’s good to know so I may not even need a new prop I just need to
clean the old one yeah I will try that first
yeah you know start spending money I hear you so it doesn’t even it’s not
like it needs a three blade fifteen by twelve Oh the advantage of the three
blade is punching into heavy wind and heavy seas it’ll keep the boat speed up
thirty percent better than a two blade that’s okay alright if you didn’t have
problems before with the two blade you know just going up an inch of pitch
would solve would get you back to where you were and from the fixed blades
perspective if you want you can just have somebody Bend an inch of pitch into
that blade if you’re not happy with how it loads of the engine pull it have a
prop stop been an inch of pitch into it and you’d be the difference between that
one point eight to one and the two point one to one so yes we’d make it a fifteen
by 13 by 13 exactly alright so tomorrow the boat haul and propeller is going to
be clean very professionally and thoroughly and then I’m going to take
the boat out again before I move and do anything regarding a new propeller you


  • Reply Mike Mc March 31, 2019 at 11:00 pm

    Interesting outcome. Just whack it till it works.

  • Reply Gerard Wall March 31, 2019 at 11:06 pm

    Hi Vin & Amy down here in Southern Australia, we’ve had a hot summer and water temperatures have been high – 28 degrees C! I had our boat Antifouled about 13 months back but when I last took the boat out it behaved poorly. I would normally be 5.5 knots at 2000rpm but at 2500 rpm I couldn’t even get 3.5 knots. In short, lifted the boat and the bottom and propellor were a real mess – not what you would expect after 13 months. After an Antifoul and propspeed to the sail drive, I now have nearly 6 knots at 2000 rpm. Your problem may be similar.


  • Reply Frank Rice March 31, 2019 at 11:17 pm

    Part of learning you guys are doing great

  • Reply SV Barry Duckworth March 31, 2019 at 11:36 pm

    Sounds like the guy was saying you were over propped before and you simply got used to the feel of that because that was all you ever knew with this boat.

    Being overpropped is really bad for the engine as the guy on the phone said.

    I think that you should maybe get a second opinion or three but get that bottom and prop cleaned and re-learn to dock that boat using a little more throttle when necessary to generate the thrust that you need.

    Thrust is the word you need to use here, not power. Your engine and prop are generating less thrust at a given RPM but you should still have the same max thrust at the top of the RPM range. Your engine will last a lot longer when you are propped correctly to match the power curve of the diesel engine to the thrust needed to move it along.

  • Reply pate allan March 31, 2019 at 11:49 pm

    yeah, yeah, yeah…. I heard the same ole story from my prop shop. The trouble is that there are different styles of 3 blade props too. A sailor man style is a thin blade and I bought one and had it installed. Boy what an expensive lesson. The yard said I was over loading my engine too because it wouldnt reach the 3,000 rpm's. I tried my new prop and its performance was so bad I felt dangerous. Then I bought a power prop which was the same as the original I replaced. I'm changing props like socks. Now I'm back to the original. I only like to run it at 1,500-1,800 rpm's anyway. Bottom line is that you dont really know whats its going to do until you try it on a sea trail. I think your on the right tract getting your prop re pitched up 1 inch. I dont think a couple barnacles would make that huge of a difference. Your prop looked pretty good to me. Its just the cost of removal and replacement. Its not fun.

  • Reply Willow March 31, 2019 at 11:52 pm

    Take the boat out for a spin after you get it cleaned, you should know what rpm your hitting at WOT (wide open throttle) with the new transmission, not what rpm you run it at. Do this before you spend money.

  • Reply Ted Facteau March 31, 2019 at 11:53 pm

    Please have the diver check the key in the propeller hub/shaft. Have diver try to turn propeller while transmission is in gear. I had a key fail before , propeller still turned but shaft was turning inside propeller hub. Very similar situation to what youre going through.

  • Reply IntermittentSailingWithKids April 1, 2019 at 12:09 am

    Get a second opinion. Maybe even a third. 2 blade props are better for overall boat speed while sailing, but 3 blades are better at getting you out of trouble. However a 3 blade prop is like dragging a bucket, but you may not care. If you go folding or feathering, stay away from Kiwi, two people in our marina had their Kiwi fall off due to a design flaw. Feathering is a NICE compromise for price vs performance under sail.

  • Reply Sailing With Vampires April 1, 2019 at 12:11 am

    Vin you need a three blade prop! You need to push through the water with crap on your hull!!

  • Reply Erik Williams April 1, 2019 at 12:36 am

    A Thornycroft T 90 is NOT a 3000 RPM engine.

  • Reply Robert Garbe April 1, 2019 at 1:17 am

    Campbell Sailers are awesome.

  • Reply Robert Garbe April 1, 2019 at 1:25 am

    Oh boy, the way you were coming out of and into the slip seemed really strange. Were you not able to steer? Like the prop person was saying, the change of transmission should not have made a huge difference, but something sure is. The thing he said which is really important is that with a clean bottom you should be able to get to 3000 rpm at wide open throttle and that is how they size props in the first place. AND a three blade is better than 2. Good luck.

  • Reply Pierre Mitham April 1, 2019 at 2:03 am

    take a step back. Your prop isn't fouled by much, just looks like normal growth. If you're seeing a significant drop in performance I would start with simpler tests. You can easily test your trans while still at the slip, no need to go out until you're sure the performance is closer to what you want. Yes a 3 blade prop is going to give you more push, but keep in mind that it also means more drag when sailing and the boat worked fine for close to 30 years with the prop that its got.

    Go back and check the basics. (keeping mind that the prop will be spinning 10-15% slower ) make sure that its fully going into gear. disconnect the shift cable from the trans and manually shift it into gear and see how much water the prop pushes while tied up (with springs) at the dock. also check that the trans is fully going into gear. You should feel a "click" at the lever when it goes into gear and with the engine running there should be a bit of a "thump" as the gear engages. You can do this for fwd and reverse while at the dock. (no need to have a crisis in the fairway) . I'm willing to bet that there is an adjustment issue with the shift lever here.

  • Reply spencer marshall April 1, 2019 at 2:37 am

    Unfortunately your hull speed will no doubt take hit sailing with a larger prop.

  • Reply Rottingboards April 1, 2019 at 3:27 am

    Thanks for taking the time to post your issues. I hope cleaning takes care of the issue. Your videos are a wonderful way to learn.

  • Reply Bob Haskin April 1, 2019 at 3:27 am

    Boy if it was my limited funds, I would go with a properly pitched 3 blade prop that gets the engine RPMs into its happy space and be done with it.

  • Reply Greg H April 1, 2019 at 4:09 am

    Gators not going to eat you hahaha

  • Reply Chuck Klima April 1, 2019 at 4:11 am

    If you do decide to buy a new prop, I can recommend the Campbell Sailor. I've had mine (3 blade) for about 2 years, and it works great. The guys at West by North were dead on with their size recommendation and my top rpm is right at spec for my engine. Good luck!

  • Reply John Malloy April 1, 2019 at 4:26 am

    Awesome+. Love your perseverance!

  • Reply John Jamieson April 1, 2019 at 4:38 am

    Well, from the looks of the existing prop, I would recommend a good cleaning before investing in a new prop. The new transmission may have a lot more to do with your loss of power than the prop.

  • Reply Michael Zakharoff April 1, 2019 at 5:27 am

    You need to really make sure your prop and skeg are fine. Pull the boat out of the water, clean it, and remove and thoroughly inspect the prop. They are known to crack. Inspect the cutless bearing. If it all checks out, and your old prop is fine, then take it out for a serious test drive. If you need to change the prop, you can use a diver to do that. Removing the prop previously should make it easy to switch props later.

  • Reply Graeme Henderson April 1, 2019 at 5:44 am

    Vin's face is looking thinner! How's the weight challenge going? The propellor info was really helpful.

  • Reply Lorne Serpa April 1, 2019 at 8:26 am

    Boat propeller guy sounds right. I've had a lot of power boats and only one sail. My opinion isn't that valuable, but 1 inch pitch wont make much difference at all. Your hull isn't dirty enough to make a difference at all in the marina, your not moving much at all. Even a dirty square box can be moved easily at low speeds. Cleaning is good, but don't expect maneuvering at part throttle/low speed in the marina to change at all. Also, the diff in pitch probably wont do anything if its only off by one inch. Its a good thing to not lug your motor per the propeller guy, but in the marina, it probably wont make a difference at all. I hope people come up with an idea to help. Is the new clutch plate slipping? In a car…a slipping clutch would leave you short on power, but only under a load; in a marina at just over idle, not much load. Maybe someone with more experience can test drive your boat for a 2nd opinion (that is a free option). I'd swap option 2 and 1. Take it out for a spin with someone to evaluate (friend fellow sailor). I.e. your boat isn't any more dirty than before this problem started a couple months ago so I doubt a dirty hull suddenly makes you under-powered or handle badly. The only thing you changed was the transmission……and now it doesn't perform well.

  • Reply Sean April 1, 2019 at 10:24 am

    i have a two blade on my J30 and any amount of hard growth on it kills any performance significantly. if your cruising I'd suggest a three blade prop.

  • Reply Chase Mixon April 1, 2019 at 11:01 am

    The last call sounded correct to me… 🙂

  • Reply David Bailey April 1, 2019 at 11:10 am

    Plan looks good. Jean Luc would say, "Execute". Get that new chartplotter yet?

  • Reply lildeena1 April 1, 2019 at 11:58 am

    Propellor place aka prop shop

  • Reply AndTheCorrectAnswerIs April 1, 2019 at 12:20 pm

    Some people will always try to sell you something new no matter what. Others will give you honest information even if it doesn't mean a sale today. If it does come time to spend money, always do business with the honest guy.

  • Reply Wayne Reeder April 1, 2019 at 12:28 pm

    Why not while the hull is being cleaned, go ahead and have the prop removed, get it repitched and reinstalled. regardless of a fouled hull your pitch is still off.

  • Reply Raymond Mills April 1, 2019 at 12:58 pm

    Has anyone ever been attacked by an alligator while cleaning their boat bottom? IMHO- you need a new propeller, period.

  • Reply Bud SV/Journey April 1, 2019 at 1:09 pm

    I enjoy. your vids and thanks for sharing your adventure.

    A few thoughts based on my prop experience on a full keel sailboat…

    The boat came with a fixed 2 blade prop that had the wrong pitch for my motor and gear ratio. I sent the prop out and had 1 inch added along with general servicing. The result was a very noticeable power improvement. No question, this repair (fairly inexpensive) was definitely needed..

    Later i swapped the 2 blade for a brand new fixed 3 blade. That change added significantly improved motoring power but also introduced some unwelcome drag when under sail. I only used this prop for a few seasons.

    Now I have a 3 blade max prop. Great power in both forward and reverse (a very welcome improvement) with no noticeable drag under sail. Very pricey but worth it in terms of added performance and safety.

    If it were my call, I would have your 2 blade pulled and sent out to a reputable prop company for adjustment and servicing without delay. I would also have the bottom scrubbed (by the driver pulling the prop).. This should restore the power levels you had before the trans problem.

    However based on the amount of motoring you do, I would add a three blade folding prop to your long term “wish list”.

    Cheers and good luck.

  • Reply Robert Thompson April 1, 2019 at 2:26 pm

    Your transmission supplier did not discuss your trans gear ratio ?..They certainly should have since you are replacing an older trans….

  • Reply Mike F April 1, 2019 at 6:05 pm

    Is the vibration that occurs in this episode at 0:20 the same as the vibration that occurred at 8:24 of episode #186 The Diesel Mechanic?

  • Reply Mike F April 1, 2019 at 6:24 pm

    I agree with @Pierre Mitham 's comments from 16 hours ago. There is testing you can do at the dock. The vibrations are highly suspect and the fouling doesn't look like a sudden culprit. Please note that a good mechanic can't necessarily describe (either verbally or in written form) all the things that s/he would instantly recognize and test if they were onsite with you.

  • Reply Terry Frazier April 1, 2019 at 7:10 pm

    I believe you do need a prop adjustment/change. Either get the two blade re-pitched, or get a fixed three blade. Yes, the folding props will give you between 1/3 and 1/2 knot under sail typically, assuming a good breeze, but they do cost quite a bit more. I would go the three blade route. They just perform so much better in wind and waves, and this is the heart of it, safety. Getting to the inlet, or anchorage, or slip 30-45 minutes before the squall or storm hits can be the difference between a happy crew, or an emotionally shattered crew. Just this past month I've watched a couple of YouTube Sailors try to go through a cut in the Bahamas with a five knot current. They made it, barely. Had there been 15-20 kts on the nose, ….well you get the picture.

  • Reply Allan Haywood April 1, 2019 at 9:00 pm

    As long the water is colder than 17°C you don't really have to worry about gators. According to the research they are not that eating active below that temperature.. Just wish I could find the video..

  • Reply Ian Bevington April 1, 2019 at 9:49 pm

    Your propeller and hull didn't look too bad to me. I'm also not convinced that the transmission ratio would result in a dramatic change. Something else has changed as a result of the work carried out?

  • Reply Sheldon Penn April 1, 2019 at 10:05 pm

    Make sure the new gearbox is turning the prop in the same direction as the old gearbox.

  • Reply Vine Len April 1, 2019 at 11:21 pm

    Your prop did not look that badly fouled that it would produce a significant loss of power. I think you need a new prop due to the near gear ratio. Three blade feathering prop would be the best if you can afford it.

  • Reply Jeff Halpern April 1, 2019 at 11:28 pm


    From my observations when I was on board, the combination of the old prop and transmission did not seem to bog the engine. The engine seemed to rev pretty readily and there was no sign that the engine was lugging. When we were motoring upwind into a stiff breeze and a short chop, with the two blade prop, the boat seemed to hold its own without noticeably loosing speed or control. That would suggest that a 3 blade prop would do nothing useful since the old two-blade seemed to have adequate thrust. While the West by North comment about three-blade prop vibration is correct for boats that have their props in an aperture, it does not apply as much to props on a strut where there is less interrupted flow and turbulence.

    The issue with a three blade prop on a moderate displacement boat is drag and the issue with drag for someone like you is less about speed, and more about heel angle and weather helm in a gust. As we have discussed the Moody is not all that stable. One way that boats disburse the energy of a gust is by accelerating. When a boat has extra drag due to a fouled bottom or a prop that it was not design to sail with, it will tend to heel over more in a gust rather than accelerate. The amount of that can be minor, but it is noticeable especially since you are sensitive to these things.

    Back to advice, reading the specs on the engine it looks like cruising speed for a T-90 would have the engine turning at around 2500 to 2800 and producing between around 24 to 27 h.p. at those RPM's. My recollection is that the Moody was able to motor at close to hullspeed at around 2500 RPM. In other words, assuming losses due to mechanical friction and prop inefficiency that suggests that the boat requires around 24 hp at the engine output shaft to reach hull speed for your boat. More rpms than that, you are burning excess fuel to get a small incremental increase in speed. Given that the engine is rated for continuous duty at 3000 rpms, there are still additional rpms and h.p. available in a stiff headwind.

    What that would suggest is that the two blade propeller produced adequate propulsion for the drag of the boat and output of the engine, and that it is unnecessary to forego to the expense and increased drag (both motoring and sailing) of switching to a three-bladed prop. Two blade props tend to be more efficient than three blade props. The reason that is true is that while a three blade prop may have less slippage than a two-blade it also has greater drag due to greater leading edge area and wetted surface. The primary reason to use a three blade prop on a displacement boat is that there is inadequate room between the shaft and the hull for to permit the installation of an adequate diameter propeller. That case is especially common on very heavy displacement boats (L/D above 300 or so) where the depth of the canoe body makes it difficult to swing a full sized prop without some kind of compromised geometry.

    If you do decide to replace the prop with a two blade prop make sure that you do so with the right 2 blade propeller. Propeller manufacturers make what used to be called power props (for sailboats and heavy displacement power boats) and speed props (which were made for more normal power boats). I don't know that they are still called that today. Power props have more blade area than speed props so the power prop can develop more thrust at the same diameter and pitch. You should confirm that the 2 blade prop being specified by West by North is in fact a power prop. It looks like WxE is recommending a Campbell prop. They appear to be a non-laminar flow prop rather than the more traditional laminar flow power props like a Michigan Sailor. The Cambell prop apparently showed a incrementally small improved efficiency in the laboratory, but I don't know how the Campbell does in the real world where there are typically higher levels of turbulence than most lab tests. But my understanding is that in theory non-laminar flow props are at their best for speed props rather than power props. That theory may have changed.

    In any event, if you are 100% convinced that you would prefer to change props rather than rebuild the old transmission then you might want to try repitching the old prop. Doing the math, It looks like the propeller shaft is turning 15% slower (rpms) with the new transmission than the old transmission. (i.e. shaft speed 1190 rpm at 2500 rpm engine speed vs 1394 rpm shaft speed for the old transmission) .

    So if your old 15 x12 prop has a pitch of 12 (inches through the water per revolution ignoring slippage) the new propeller would need to have a 15% greater pitch and so would seem to be closer to a pitch of 14 than the 13 suggested in the video. The rule of thumb for powerboats used to be that a bronze prop could be repitched no more than approximately 2 inches (although there were prop companies that disagreed with doing that much for sailboats since a sailboat prop operates at a slower speed (i.e. 12 vs 20 or so) through the water and thise companiy's recommendation were more like a max of 1 1/2 inch of repitch). One problem is that you don't really know the pitch of your current prop since it may have been previously repitched already.

    So if you are 100% convinced that there is no way that you will rebuild the old transmission, and assuming the old prop hasn't been repitched, you might try to have it repitched to 13.5 (If you decide to go that route, you might want to have the diver remove the old prop when they clean your bottom.). Repitching is cheap compared to buying a new prop. You can see how you like having a steeper pitch prop with a slower shaft speed, and if it works, you are all done.
    If you don't like it, you will at least be able to get a sense of what the proper pitch should be if you do buy a new prop,

    One more thing, you seemed to like having prop walk as a maneuvering assist, (I do too). A three-blade does have a lot less prop walk. Jus' say'n

  • Reply gord pineappleexpress April 2, 2019 at 3:10 pm

    a sail boat is a hole in the sea you throw money into .

  • Reply sirlandsalot April 11, 2019 at 9:18 am

    well you guys, I followed you intensely during your shopping, finally now its my turn! We just bought a 1977 54 foot ketch and the house is rented and we are moving aboard may 1 with our 4 and 6 year old boys! we did it!!!!!,

  • Reply Walter p Curry April 13, 2019 at 1:28 pm

    You need a three blade prop.

  • Reply huey hoolihan May 30, 2019 at 3:40 am

    so when did you learn that the new transmission had a different final ratio than your old one? before or after the transmission was installed?

  • Reply Dave Brown July 21, 2019 at 1:26 am

    re build old trany keep 1.7 ratio

  • Reply Dave Brown July 21, 2019 at 1:26 am

    maybey replace cutlass bearing too?

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