The completion of the installation of the Kubota coincided with the annual antifoul so the first outing was
with a clean prop and bum. Now I know the old Bukh was tired but I didn't know how much until yesterday.
I suppose a big difference is the Bukh was raw water cooled from a 1/2 inch hose feed and when motoring
the exhaust sort of went 'donk donk splash - donk donk splash' but the kubota is heat exchanger cooled
from a 3/4 inch feed and puts out an amazing amount of water from the exhaust. The new engine is so much
more powerful that even at 'running in revs' of 2000 rpm the amount of water it pushes up at the stern is very
noticeable. My exhaust outlet is about 2 inches above waterline right at the rear on the Port side and I now
have a bit of a problem.
When the amount and force of the exhaust water meets the water pushed up by the prop I get a noise that
sounds like Niagara Falls on a windy day. When I first opened the throttle it sounded like all the bearings in
world had seized up all at once. Missus said it wasn't coming from inside the boat so I discovered the scource
of the racket and scratched my head. I don't suppose it's doing any harm but I can do without it, so I guess
the easiest solution is to raise the exhaust outlet up hull by 4 inches or so to clear the sea water, other than
that ....I don't know. Any suggestions ??.
Sounds like you've made yourself a speed boat Sam! Moving the exhaust outlet up might be necessary by "sound" of it. They do that on ski boats.
Select to expand quoteTrek said..
Sounds like you've made yourself a speed boat Sam! Moving the exhaust outlet up might be necessary by "sound" of it. They do that on ski boats.
Ski boats eh Trek. That's interesting, and here's me thinking I'd had an original thought about raising the outlet.... Ha.
Sam
My first thought is to give it a while and see if you get used to it.
Not likely.
Moving the exhaust outlet up will work in solving you gurgling noise problem.
The outlet on my old boat was a good 35 cm above the water.
Rust stain down the hull and black soot stains were the result, but I didn't have your noise irritation.
The question/are, can you do it yourself in the water and how much will it cost for you to do it or have it done?
Gary
Thanks guys.
Gary. I've come to the conclusion that raising the outlet is the easiest way out of the situation.
The shipwright at the marina drilled out the old raw water 1/2 inch skin fitting and replaced it with a 3/4 inch
one ( parts supplied by me ) and plumbed in the pipe work to the engine for $215. I was happy
with the cost. Of course the raw water inlet is well under water, not so the exhaust outlet sooo
just maybe it can be done in the water, but not by me. I'll call into the marina and get the shipwright
to have a look. I will report back to you.
My exhaust outlet is under water giving a gentle gurgling sound reminding one of the fact that the sea-cock is open and the impeller working correctly.
It has the appropriate exhaust elbow inside, and a pong box, to stop flooding, of course.
No streaks of soot on the hull either.
Select to expand quotesirgallivant said..
My exhaust outlet is under water giving a gentle gurgling sound reminding one of the fact that the sea-cock is open and the impeller working correctly.
It has the appropriate exhaust elbow inside, and a pong box, to stop flooding, of course.
No streaks of soot on the hull either.
If it was a gentle gurgling sound SirG I wouldn't worry about it but my boat sounds like a gang of banshees going off
and I don't think I'm going to be able to live with it.
The underwater outlet muffles sound. I am glad, my boat has one.
My mates Cav 32 with the outlet well above water is rather unpleasantly noisy.
The other boat l was racing on (had a single cyl. Bukh motor) had underwater outlet and it was pleasant.
I hope, you can solve this unpleasant situ before you burn the boat.
Select to expand quotesirgallivant said..
The underwater outlet muffles sound. I am glad, my boat has one.
My mates Cav 32 with the outlet well above water is rather unpleasantly noisy.
The other boat l was racing on (had a single cyl. Bukh motor) had underwater outlet and it was pleasant.
I hope, you can solve this unpleasant situ before you burn the boat.
The single pot Bukh I had was not a problem because it didn't spit out enough water to make a noise. This Beta however
chucks out a ton of water and the noise appears to be caused by the exhaust water competing with the sea water for
the same space. If I raise the exhaust outlet it will at least give the exhaust water somewhere to go. No doubt I will get
a splashing sound as it drops into the sea water but it's got to be a whole lot quieter than what's going on now.
It seems that I am over propped. The prop that I have on now is a 3 blade fixed 13 x 10.5, how
the old Bukh ever turned that is a mystery. Porters have just told me it should 12 x 8 and they
will alter it, no problem. Should I do this or should I leave it as it is considering I now have a
bigger engine that will cope better with a big prop.
Select to expand quotesamsturdy said..
It seems that I am over propped. The prop that I have on now is a 3 blade fixed 13 x 10.5, how
the old Bukh ever turned that is a mystery. Porters have just told me it should 12 x 8 and they
will alter it, no problem. Should I do this or should I leave it as it is considering I now have a
bigger engine that will cope better with a big prop.
Sam the calculations should have included the boat type and the engine size and output. If in doubt ask a few other suppliers and see if their suggestions are the same or similar .
I think the gearbox ratio is also pretty important. Just bought a new prop from Flexofold and they won't advise on the right size without it.
Porters were the people who made the prop based on the the boat specs and engine/gearbox specs. The Bukh
gearbox was 2.5:1 the Beta is 2;1. How ever Glen ( at Porters ) was scratching his head at why the prop is that size.
So now I'm wondering if my noisy exhaust problem is caused by the over size prop pushing too much water up
to the stern whereas the boat is designed for a smaller 12x8 prop and the outlet will be above water level.
Put a shower head on your exhaust 
If possible try a temporary extension to your exhaust, try higher and under water, that way you take the guesswork out before you spend $$$ on what may not be the best out come.
Select to expand quoteCraig66 said..
Put a shower head on your exhaust
If possible try a temporary extension to your exhaust, try higher and under water, that way you take the guesswork out before you spend $$$ on what may not be the best out come.
How would you do that without drilling a couple of new(unwanted) holes in the hull? One for the higher test exhaust and one for the lower.
Select to expand quotesamsturdy said..
So now I'm wondering if my noisy exhaust problem is caused by the over size prop pushing too much water up
to the stern whereas the boat is designed for a smaller 12x8 prop and the outlet will be above water level.
HI Sam,
Makes perfect logical sense to me. You never know, you may just fix the root cause and not a symptom.
If it turns out like that, nice work Watson!
Select to expand quotesamsturdy said..
Porters were the people who made the prop based on the the boat specs and engine/gearbox specs. The Bukh
gearbox was 2.5:1 the Beta is 2;1. How ever Glen ( at Porters ) was scratching his head at why the prop is that size.
So now I'm wondering if my noisy exhaust problem is caused by the over size prop pushing too much water up
to the stern whereas the boat is designed for a smaller 12x8 prop and the outlet will be above water level.
sam, for what it's worth I recon that the combination of the gear reduction ratio being seemingly not much ie .5:1 if you add that .5 to an engine input of just a few hundred rpm from the updated power plant it would I think make a huge difference.
Might be a good time for a sweet little folding prop to complete the repower
So I've decided to do this job in two stages ( 1 ) get the prop resized. ( 2 ) get the exhaust fixed. If resizing
the prop fixes the exhaust problem.....great.
In order to keep the cost down I've contacted diver Dave Pollock to take the prop off in the water. I'll take
it to D H Porter and they can resize it. Dave said to get it propspeeded before I give it to him to put back on.
It sounds good to me and should happen one day next week.
I'll keep you posted.
Select to expand quotesamsturdy said..
So I've decided to do this job in two stages ( 1 ) get the prop resized. ( 2 ) get the exhaust fixed. If resizing
the prop fixes the exhaust problem.....great.
In order to keep the cost down I've contacted diver Dave Pollock to take the prop off in the water. I'll take
it to D H Porter and they can resize it. Dave said to get it propspeeded before I give it to him to put back on.
It sounds good to me and should happen one day next week.
I'll keep you posted.
Can you get a second hand prop to see if a different size removes the noise?
You may be on to the answer and then upgrade.
Select to expand quoteBundeenabuoy said..samsturdy said..
So I've decided to do this job in two stages ( 1 ) get the prop resized. ( 2 ) get the exhaust fixed. If resizing
the prop fixes the exhaust problem.....great.
In order to keep the cost down I've contacted diver Dave Pollock to take the prop off in the water. I'll take
it to D H Porter and they can resize it. Dave said to get it propspeeded before I give it to him to put back on.
It sounds good to me and should happen one day next week.
I'll keep you posted.
Can you get a second hand prop to see if a different size removes the noise?
You may be on to the answer and then upgrade.
Well Bunny, the way I see it, regardless of whether resizing the prop fixes the noise, the prop is still too big
for the engine, 13x10.5 is significantly larger than 12x8 and I need to get it to the right size regardless of any
other problem. Perhaps someone can tell me the consequences of using a prop that's far too big.
I'm just hoping that my thinking about too much water being pushed up is correct and the resizing will fix it.
We'll see.
Select to expand quotesamsturdy said..Bundeenabuoy said..samsturdy said..
So I've decided to do this job in two stages ( 1 ) get the prop resized. ( 2 ) get the exhaust fixed. If resizing
the prop fixes the exhaust problem.....great.
In order to keep the cost down I've contacted diver Dave Pollock to take the prop off in the water. I'll take
it to D H Porter and they can resize it. Dave said to get it propspeeded before I give it to him to put back on.
It sounds good to me and should happen one day next week.
I'll keep you posted.
Can you get a second hand prop to see if a different size removes the noise?
You may be on to the answer and then upgrade.
Well Bunny, the way I see it, regardless of whether resizing the prop fixes the noise, the prop is still too big
for the engine, 13x10.5 is significantly larger than 12x8 and I need to get it to the right size regardless of any
other problem. Perhaps someone can tell me the consequences of using a prop that's far too big.
I'm just hoping that my thinking about too much water being pushed up is correct and the resizing will fix it.
We'll see.
Sam, not my area of expertise but I always thought that if the engine can be run at its design full revs then the prop is about right, an oversize prop will bog down the engine and not allow it to reach it's potential. Is this the case with your's ?
Select to expand quoteUncleBob said..samsturdy said..Bundeenabuoy said..samsturdy said..
So I've decided to do this job in two stages ( 1 ) get the prop resized. ( 2 ) get the exhaust fixed. If resizing
the prop fixes the exhaust problem.....great.
In order to keep the cost down I've contacted diver Dave Pollock to take the prop off in the water. I'll take
it to D H Porter and they can resize it. Dave said to get it propspeeded before I give it to him to put back on.
It sounds good to me and should happen one day next week.
I'll keep you posted.
Can you get a second hand prop to see if a different size removes the noise?
You may be on to the answer and then upgrade.
Well Bunny, the way I see it, regardless of whether resizing the prop fixes the noise, the prop is still too big
for the engine, 13x10.5 is significantly larger than 12x8 and I need to get it to the right size regardless of any
other problem. Perhaps someone can tell me the consequences of using a prop that's far too big.
I'm just hoping that my thinking about too much water being pushed up is correct and the resizing will fix it.
We'll see.
Sam, not my area of expertise but I always thought that if the engine can be run at its design full revs then the prop is about right, an oversize prop will bog down the engine and not allow it to reach it's potential. Is this the case with your's ?
Not currently Bob because I'm 'running in' I'm only allowed to go to 2000 rpm. Nonetheless the engine may be
stressed without me knowing it yet and I don't want to ruin a brand new engine.
Looking back at the time the Bukh was in and thinking about how that ran I think it's safe to say it did not rev
freely, but, with a single cylinder donk with such a long stroke it may be hard to determine especially when you
have as little experience with them as I have.
Sam, Glen at Porters is an expert on this. Trust his advice with confidence.
If he specified this prop with the engine and gearbox on your boat it is unlikely he got it wrong. Possible but unlikely. If he did he will own up to it.
What hp is the new engine compared to the old?
My take on this issue is that if you have gone up in power considerably you will find the stern will squat down a lot more and may put the exhaust under the water when before it didn't. If the exhaust was designed to be submerged that is fine but if it wasn't, like mine isn't and it sounds like yours wasn't, when it submerges it can be noisy and create back pressure that reduces performance and doesn't do the engine any good over time.
I saw an S&S34 some years ago with a 30hp donk, at cruising power the stern was nearly underwater. Way overpowered and when the boat was sold on the new 30hp engine was removed and a 24hp put in, somebody probably wasted $20,000.
Having put the new engine in you will want to be at cruising revs most of the time. If the stern is too low in the water just raise the exhaust outlet. One hole to be drilled, one filled and a bit of exhaust pipe.
Yes MB, I've already spoken to Glen so when I take the prop down to him I'll also take all the original info regarding
boat and engine ( I still have it all including the receipt for the prop he made ) plus the info on the new engine and he can work it out from
there. He's not going to make a new prop, He says he can cut down this one and alter the pitch. That'll do me.
Sorry MB I didn't answer the HP difference. The Bukh was 10 hp single pot, the Beta is a 14 hp twin.
Select to expand quotesamsturdy said..
I'm 'running in' I'm only allowed to go to 2000 rpm.
I would be talking with Kubota about that. Diesel engines love "load".
If you nurse that engine you will surely glaze the bores. This "running in" idea/proceedure is not generally relevant today.
Engine manufacturers have figured it out and no longer make engines to the size tolerances that require a "running in" period. They deliver engines "ready for work".
You are "allowed" to run the engine at whatever load capacity you "choose". Of course running it as the manufacturer recommends is recommended for warranty purposes.
Beta is not the manufacturer of the engine. Kubota is. Read your warranty document carefully.
Select to expand quotecisco said..samsturdy said..
I'm 'running in' I'm only allowed to go to 2000 rpm.
I would be talking with Kubota about that. Diesel engines love "load".
If you nurse that engine you will surely glaze the bores. This "running in" idea/proceedure is not generally relevant today.
Engine manufacturers have figured it out and no longer make engines to the size tolerances that require a "running in" period. They deliver engines "ready for work".
You are "allowed" to run the engine at whatever load capacity you "choose". Of course running it as the manufacturer recommends is recommended for warranty purposes.
Beta is not the manufacturer of the engine. Kubota is. Read your warranty document carefully.
Well picked up Cisco.
I was thinking the same thing but don't know the particular engine so didn't want to say anything that could mislead. An old stoker is better placed to pass comment than an old birdie.
The need to run the engine under load was also behind my thinking to get the exhaust clear of the water so Sam can run the engine at the right revs. Running it at low revs to avoid putting the exhaust under would not be a good option for the engine.
I just got back from having the day off yesterday ( watching my granddaughter at a dance comp. ) Regarding
engines 'under load', pushing a boat along at any revs would put an engine under load, would it not ?. I thought
glazed bores were caused by running the engine to only charge batteries and doing it at too low revs.
Cisco, I guess I'm trusting Beta ( through their handbook ) to give me the same advice as would come from Kubota.
Sam, your engine booklet should have a graph of it's torque curve.
The RPM at which it achieves maximum torque is where it will run best regarding engine wear in the bore AND where you should achieve the best fuel economy. You should be able to run it at that speed 24 hours a day with no problems. That speed will be where you achieve maximum continuous rated horsepower.
Maximum horsepower will be at a higher RPM but the engine should only be run at that speed for probably no more than one hour.
Essentially what you have is an industrial engine such as you will find powering welding machines, lighting plants and air compressors. There are thousands of them around. The are designed to run at a continuous speed and load.
As far as warranty goes it obviously behooves you to stick to the manufacturers recommendations. It may be worthwhile comparing what Beta and Kubota have to say.
As far as your doubts about exhaust and propellors go, I would run the engine at maximum torque speed and observe what happens then. If there is black smoke from the exhaust it is more than likely that the prop is over pitched.
The Beta may run better without a water trap/muffler. The water injection muffles the exhaust anyway. An anti siphon loop will probably suffice.
Yes you are right Cisco. The graph shows max torque at 2600 rpm with a fuel consumption of one and a half litres per hour.
Now that's almost the revs they're telling me not to exceed for 20 hrs, so it looks like there will be no harm done sitting at
maximum torque when I get going again.
Regarding the exhaust situation, it also states that the exhaust back pressure should be kept to a minimum, so that means
no under water exhaust as that will dramatically increase back pressure. So, going along with resizing the prop to correct
size to keep the exhaust outlet above water seems the right thing to do.
