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Old 01-02-2018, 08:53   #16
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Re: Pulling the trigger on new motor...help please.

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Originally Posted by nzmal View Post
My wife and I are about to put the deposit on a new engine for out Cavalier 39 yacht.
Specs are
GRP 9 Ton displacement
LWL 29'6"

She still has her original 1975 Volvo MD3B 36hp engine which is well tired now.

We're sold on a Beta but hovering between a 43 and 38.
The 38 weights 100kg less and is slightly cheaper (but not cheaper enough for that to be a factor)

We're currently running a 16" three blade prop on the Volvo but its left handed so a prop change is required.

The 43 will require an 18"
The 38 will use another 16"

We initially thought that the boat wouldn't take an 18" prop but just read the original spec sheet and see that it originally was fitted with an 18 inch 2 blade.

...because of the prop sizing we'd decided the 38 was the way to go, but now that it appears we can fit an 18 inch the 43 is back on the table....


.....arghhhhh.

Is there likely to be a huge difference in performance taking the 43 over the 38? Can anyone provide me with some sensible thinking here?

Thanks
Mal (New Zealand)
I hope by fitting you have included the amount of clearance required to be efficient not just he physical clearance.
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Old 01-02-2018, 09:45   #17
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Re: Pulling the trigger on new motor...help please.

Faced with the same choice of two possible beta engines I opted for the larger lower rev choice (1505). Reasoning was that it would give better fuel economy and more reserve power which was important as I wanted the motor as backup in heavy weather. Mine worked out at 4.5hp per ton on a traditional long keel design with a 15" 3 blade prop. Worked very well, I get 5kn @ 1800rev and less than 1.5lt/hr in mod or less sea state. It is certainly plenty and I would not go above 4.5hp/ton. When I talked to Beta (UK) their question was "what do you want the engine to do". It is a very good question. My answer was "power the boat to windward in 30kn" If I had said" keep me moving when the wind dies the recommendation would have been for a much smaller engine.
(now replacing it with the same one but that is because it got flooded)
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Old 01-02-2018, 11:48   #18
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Re: Pulling the trigger on new motor...help please.

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Hi Jim
Prop hasn't been determined except it will have to be fixed blade since there isn't room for a folding one. Probably be a 3 blade 16 or 17 inch. I'll let the prop expert give that advice.
If you've got lot's of money you could go for a feathering variable pitch prop.
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Old 01-02-2018, 12:35   #19
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Re: Pulling the trigger on new motor...help please.

I plan to repower my Scout 30 this year with a Beta. I had a good talk with Stanley at the St Pete Boat Show. It seems the Betas burn fuel so efficiently that you can run the motors at low rpms for extended periods with no adverse effects as long as you don't over prop them. What that means is that you can cruise the bigger engine at lower rpms most of the time but still have the reserve power for punching into a head wind.
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Old 01-02-2018, 14:18   #20
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Re: Pulling the trigger on new motor...help please.

I went from a Westerbeke W-52 to a Beta 60 on a much heavier boat and haven't regretted it, but that was in the context of a complete drivetrain replacement from a second power take-off to going to a four-bladed feathering prop.

One hundred kilos is a lot to lug around. The key word here is "lug". You want to do the calcs to determine that your new prop (whether 16 or 18 inch) is well-matched to your output of the engine you choose: I am flattening my pitch by one inch to raise my WOT RPM to the designed values as I am "lugging" slightly.

You also want to factor in the size of your battery bank and your charging sources: would you want a larger alternator and will its load deprive you of needed HP when you need it most? Given your displacement, I think you could safely go with the 38 HP and enjoy the lower fuel consumption, more room around the block to access things and less weight. But it's a suite of interlocking considerations: I do not think of "now I have eight more horses to play with" so much as I think "I can safely put it a higher-output alternator to charge my house bank and that means a watermaker, too". You're on the right track with a Beta, however.
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Old 01-02-2018, 14:35   #21
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Re: Pulling the trigger on new motor...help please.

Are you sure about the 9 tons or is that manufacturers weight.My boat listed at 7.5 ton but with all gear aboard and empty water and black tanks and full fuel I weighed 10 ton.Repowered from a westerbeke 33 to a Beta 38 and am totally happy unless I am bucking high currents and head winds so my advice is go as big as you can with the limiting factor being space.JMHO
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Old 01-02-2018, 14:46   #22
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Re: Pulling the trigger on new motor...help please.

Hmm...

Above we have a lot of amateur opinions and one professional one (post 12).

I know whose advice I would take!

Jim
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Old 01-02-2018, 15:23   #23
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Re: Pulling the trigger on new motor...help please.

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Hmm...

Above we have a lot of amateur opinions and one professional one (post 12).

I know whose advice I would take!

Jim
You are totally right Jim but the main word in 12 is assuming which from my experience with a boat is not a good practice and that was all I was trying to get across on my post.
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Old 01-02-2018, 19:28   #24
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Re: Pulling the trigger on new motor...help please.

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Hmm...

Above we have a lot of amateur opinions and one professional one (post 12).

I know whose advice I would take!

Jim
Here's what Stanley said, "You should achieve just over 7 knots in flat water and you will enjoy the extra space in the engine compartment when you have service work to do. The 43 with a 2:1 transmission does not show to improve boat speed at all."

Stanley knows what he's talking about & I believe him when he says you can achieve hull speed in FLAT water with the smaller motor. Most of the time that will be enough & you will be happy. In fact I'd consider the lower rpm 35 which is the same motor. However, if you want to get close to hull speed when motoring into a strong headwind you might need more power.
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Old 01-02-2018, 21:04   #25
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Re: Pulling the trigger on new motor...help please.

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However, if you want to get close to hull speed when motoring into a strong headwind you might need more power.
Undeniably true. And if you want to do so towing water skiers, you'll need even more!

One has to decide what reasonable expectations for a cruising yacht under power might actually be. Hull speed into strong headwinds isn't IMO, but different strokes...

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Old 02-02-2018, 02:14   #26
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Re: Pulling the trigger on new motor...help please.

Thanks .. to be clear. Hull speed isn’t something that I’d usually motor at. I’m happy at 5 or 6 knots. I would like to be able to motor into 30 knots when required.
Beta 38 should push me into the wind and make calm water hull speed with the right prop choice?
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Old 02-02-2018, 07:35   #27
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Re: Pulling the trigger on new motor...help please.

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Originally Posted by Jim Cate View Post
Undeniably true. And if you want to do so towing water skiers, you'll need even more!

One has to decide what reasonable expectations for a cruising yacht under power might actually be. Hull speed into strong headwinds isn't IMO, but different strokes...

Jim
How glib. I'll bet you know that the OP will never be able to pull a skier no matter how big his engine. I'll also bet that some here have been glad to have enough power to pull themselves off of a lee shore in a bad blow or to re-anchor after dragging. Personally I'd want the bigger motor not only for emergencies but because it's a 2800 rpm motor where the 38 develops that hp at 3600 rpms. That being said the 43 is really a lot bigger in size & weight. I would not go that route unless it's a good fit. You're only gaining 5hp.

You might want to have Stanley run his numbers for the 35 compared to the 38. He did that for me & there was no noticeable difference in top speed. They are the same motor but with the 35 you're developing cruising speed at a much lower rpm.
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Old 02-02-2018, 08:28   #28
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Re: Pulling the trigger on new motor...help please.

Stanley,
I have a Cheoy Lee Pedrick 41 weighs about 14T loaded. I am getting ready to replace the tired Perkins 4108 and considering a new Beta (and not a Yanmar) What recommendations and advice can you help me with in the decision. Is there a typical engine and tranny which is a relatively easy drop in and compatible with our Walters V Drive. Thanks, CR
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Old 02-02-2018, 13:10   #29
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Pulling the trigger on new motor...help please.

My boat will make 8 kts or slightly more in flat water.
Hull speed is like 7.3 kts.
However I’d like a bigger motor. My reason is because at 1500 my motor sound wise is a delight, turn it up to 1900 and it’s not all that bad, but much over that and it sounds like mating chainsaws to me. I cruise at 1900 more than anything else to keep the noise acceptable. So I’d like a bigger motor, so that most of my motoring would be done at lower RPM and the noise, vibration and harshness would be so much less.
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Old 02-02-2018, 19:29   #30
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Re: Pulling the trigger on new motor...help please.

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Thanks .. to be clear. Hull speed isn’t something that I’d usually motor at. I’m happy at 5 or 6 knots. I would like to be able to motor into 30 knots when required.
Beta 38 should push me into the wind and make calm water hull speed with the right prop choice?
I think you have the right idea especially with the changeable weather here. No fun being on a lee shore with not enough power to claw your way off.
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