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Bimini Babe

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That's kinda what I was wondering Squid...

 

The boat does have a 27hp motor in it currently, but as it won't go anywhere near full revs without boiling over almost instantly there's no way we'll be getting 27 out of it. The boat does drag her ass a bit, but the new motor should be as much as 50kg lighter, which might go some way to solving that problem.

 

No major requirement for a big alternator - would be 70Amp max, as we've got a wind genny and solar panels as well. And on a 29' boat, no major plans to run a fridge off it either, although it is a possibility for the future.

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If you can't get full RPM, then you are over prop'd.

(not saying this is you BB) But Many people think it is more economical to have the motor over prop'd and run the motor at ower revs. But as BB stated above, it means yuou never get to see the full power of the engine. The Hp rating of a Diesel is directly related to the RPM it is spinning at.

A rule of thumb for power to weight is 3Hp/tonne. That gives you a small simple setup to get you in and out of the marina/mooring area and move you along. 5Hp/t is allowing you to be a "true" motor/sailor where it has equal ability in both modes and is seen more today because of the extra's the engine is being asked to run, like freezer and Aux power generation etc. It is also a good rule of thumb for displacment Launches, with their upper end being around 7Hp/t.

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If you can't get full RPM, then you are over prop'd.

 

That may not necessarily be the case wheels. BB stated that she can't get full RPM without it boiling over implying that the prop may be cavitating rather than revving out.

 

BB to give you an idea most 1020's have an 18HP, there are some with 13's and some with 27/30's. A friend of mine has a 6.5 tonne Chico 355 and it has a 30HP in it with a 90A alternator, fridge/freezer etc.

 

I'm picking you old 27HP is already producing more power than you can use. A new 25 may produce even more than you old worn out one does at the moment :?:

 

Is the 20HP option lighter than the 25 i.e. is there a penalty for carry this extra HP around that you potentially cannot use?

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Yeah you're probably right there Farrari, I reckon even a new 20hp would probably produce more power than the old one is giving at the moment! And it's got quite a big alternator on it too - 100 or 120 even, and we'll be going down to a 70 or a 40, depending on the motor and options we choose. But that's not a major problem as we now have a wind genny as well as solar panels, and to be honest not a great deal of elec equip anyway - I wanted to keep the boat pretty simple.

 

25hp is 113kg, 20hp is 104kgs, so not a major increase in weight.

 

Prop was the smallest size we could get at the time - 15.5in Kiwiprop. I've since been told they've now gone down to 14.4in blades, but don't really wanna replace them if I can avoid it.

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Prop was the smallest size we could get at the time - 15.5in Kiwiprop. I've since been told they've now gone down to 14.4in blades, but don't really wanna replace them if I can avoid it.

 

Kiwiprops are MOST helpful. Based on the Northern side of Mt Wellington, Panmure; so easy to visit but best to phone first.

It may be possible to just get smaller blades and fit them at next haulout or on the grid between tides at minimal cost. Further you would have spare blades "that you know will fit" if needed at a later date on your world cruise.

 

Changing the blade size will also change loading on engine, and may have other implications e.g. higher RPM, more or less cavitation, fuel consumption etc. but I am no expert in this.

 

Before you depart, it could be wise to remove you prop and take to Kiwiprop for a full check over / service. I know that the material used for the plastic boss has changed for a harder one. They have serviced two yacht's props that I sail on and were most helpful.

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The rattling noise is pretty standard for a Kiwi Prop is because the blades are not a very efficient shape, with no cupping or twisting of the baldes to account for the outer part of the blade moving alot faster than the inside.

Sounds like you may want to adjust the pitch of your prop, easily done on a kiwi prop by backing the pitch screw out, just make sure it is an even amount on each blade, I have found half a turn increment at a time is a good amount to adjust.

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Cavitating... interesting thought. Replaced P-bracket bolts last year as it was pretty wobbly, but it still makes a hoor of a rattling noise when engine at low revs...

 

I have the same prop on mine and it doesn't make any noise at low RPM. I do get a harmonic through the hull at higher RPM however. The idle speed in mine is also adjusted a little higher so as the motor doesn't stall when going into reverse.

 

I'd echo PaulR's comments - talk to Kiwprops as they have been helpful to me in the past.

 

Also on your motor choices, a 40A/H alternator would seem a little small these days. You may want to work out a battery budget to double check that this will be sufficient, especially if you have a 100+ one at the moment. An alternators rated value is based on ambient temperature. The higher the temperature the less it will put out. Some are not rated as continuous output so can only put out the rated value for a small period of time.

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I missed the Cavitation part somewhere. That must have been said earlier or I am blind.

Overheating can be a sign of over prop'ed or of course, a cooling problem.

The rattling noise is pretty standard for a Kiwi Prop is because the blades are not a very efficient shape, with no cupping or twisting of the baldes to account for the outer part of the blade moving alot faster than the inside.

That woudl be the first I have heard of a "rattly" Kiwi Prop.

The shape is because they are a completely different design and they are very efficient. That is what is making them such a choice for many boaties. They are an excellent prop and should be quiet. Because of their unique shape, many new user comments are often that they have lost the problem of "prop walk" and another comment is often about how well they stop the boat.

The only issue I have with them, is that they don't make a prop big enough for my boat.

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Spoke to John at Kiwiprop yesterday in fact - he is indeed a top bloke - always helpful. And he did suggest winding back the pitch a touch when I put the new motor in.

 

To be honest I'm well beyond even caring what the problem is with my current engine - overheating, loss of power, failing to start, stalling in idle... I don't even care about the cause any more, I just want shot of it. As soon as one problem is fixed, another one appears. It could be the head. It could be piston rings. It could be a whole number of things, but chances are it's probably everything. And I'm fed up throwing good money after bad on it.

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By the way Wheels you may want to speak to John if you haven't in a while - seems to be expanding his range a bit - it was him that told me about the new smaller blades, so perhaps he's making bigger ones too, or may not be far off?

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but chances are it's probably everything.

Yeup, with Diesels long in the tooth, that is often the case. Fixing one problem often leads to another. The entire engine wears away altogether and if one part is fixed, the load sometimes upsets the balance so to speak.

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I missed the Cavitation part somewhere. That must have been said earlier or I am blind.

Overheating can be a sign of over prop'ed or of course, a cooling problem.

The rattling noise is pretty standard for a Kiwi Prop is because the blades are not a very efficient shape, with no cupping or twisting of the baldes to account for the outer part of the blade moving alot faster than the inside.

That woudl be the first I have heard of a "rattly" Kiwi Prop.

The shape is because they are a completely different design and they are very efficient. That is what is making them such a choice for many boaties. They are an excellent prop and should be quiet. Because of their unique shape, many new user comments are often that they have lost the problem of "prop walk" and another comment is often about how well they stop the boat.

The only issue I have with them, is that they don't make a prop big enough for my boat.

 

The rattle is a cavitation type noise not a vibration and happens at low revs when

in forward it goes away as soon as revs are increased, my last boat did the same thing once converted to a kiwi prop and a friends boat does the same. The prop actually incresed prop walk on both of my boats but I still love them for the sailing and reversing performance, the are a very clever design but i'm pretty sure they are not as good under motor as a non feathering prop.

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Aaaaaaaaaaaaand..... it's GONE!!!!!!!!!!! :D :thumbup: :D :thumbup: :D :thumbup: :wave:

 

http://www.trademe.co.nz/motors/boats-marine/parts-accessories/engine-parts/auction-392828585.htm

 

Ordered my new Beta from The Engine Room today. Happy bunnies.

 

If anyone is intersted in my old Daihatsu (God knows why you wouldn't - I've talked it up enough here...), or any bits off it, feel free to PM me questions or offers. I will of course pay the obligatory rum funds to Squid on any sales made here! :D

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