Through holes and prop
- Thread starter PK123
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- through-hulls thru hulls
From the listing I posted earlier:
As for the distance between the hub and strut, our experiences differ.
The boat is at Crescent Beach Marina, the location listed in the OPs info. Some Mirage 27s were built with an OMC Gas Sail Drive. See this old listing. Given what we know about the boat, it seems quite likely the original engine was a sail drive.
As for the distance between the hub and strut, our experiences differ.
I sure hope the boat in the listing is not what the OP is looking at.But I may have found some information.
There is a Mirage 27 for sale at Crescent Beach Marina, which matches the OP location and boat description. In the listing it is noted that the boat has been repowered. See link to listing below.
Details : Crescent Beach Marina
crescentbeachmarina.com
The listing says "Boat is in excellent Condition. Ready to go Sailing" and the pictures show what looks like a nice clean bottom. Clearly not consistent with the OP's photos. Maybe an old listing?
Well, maybe the OP's pictured boat is ready for sailing but certainly not ready for motoring!
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My production Starwind 27 (Wellcraft production) had a gap of about 3" to 4" between the front of the hub and the strut. I just looked at a picture of it. I don't have a picture of my Catalina but I'm pretty sure that it is not just an inch. I'd guess from memory that it is about 3 to 4. I'm curious now. My initial reaction when I saw the picture was that it did look like a little bit too much spread, but I agree, it's hardly anything to quibble about. The base of the strut does look like a fugly installation now that I look more closely.
Other than the prop, I don't see anything that looks really bad. To me, it looks like a nice clean bottom that has just come out of the water ... it looks wet, like it hasn't even been pressure-washed. What am I missing? It looks good to me.
If that depression is a patched hole for a sail-drive, so what? If it's the same boat as the listing, which has a new Yanmar 2YM15, I consider that a huge PLUS! Replace an old OMC sail drive with a new Yanmar 2YM15??? .... Count me in! (They do come in saildrive as well so why wouldn't they replace in kind if that was the case?) I'm still not convinced the hole is from a saildrive. The shaft hole looks fine to me and I don't even know that it would be feasible to drill a hole at that angle for a new installation that cleanly.
It just goes to show that there are a lot of unanswered questions before dismissing this boat. Replacing the prop, or even the shaft and strut (if necessary) is simply not that big a problem if the boat is in good condition and the price is right otherwise.
As for going to the effort and expense for a 27' sailboat?!? I can relate ... when I add up all the improvements to my Starwind, that I bought for $8,500 (15 years before I sold her), I spent at least 6 times the purchase price (not including slip, storage and insurance fees!) on improvements. That includes a re-power with Yanmar 2YM15. I'll vouch that is a huge improvement on a 27' boat!
I'd like to hear more from @PK123 ... I hope he is taking a close look at her and getting answers to his questions!
If you did want to reduce that space, why not just shorten the shaft? Only have to worry about the prop-to-hull clearance, which should be no less than 1", I think.
@Scott T-Bird its been really interesting evaluating everyone's comments - thanks to everyone for sharing their knowledge, concerns and good advice.
The background was that the owner was not able to attend to the boat during covid and the marina has quite a bit of stray current. He hadn't placed zincs on the prop shaft after its last haul out from 2 years ago (the sales photos on the Crescent Beach Marina web site). He was shocked to see the condition of the prop as anyone and has replaced it free of charge. The thru hulls I inspected inside and out and had a good poke around with a screw driver. There are some minor metal fragments that dislodge out of the side wall when poked from the underside but they are actually in reasonable condition as are all the seacocks - a tiny bit of green corrosion on the brass but the valves all turn with ease. The owner has agreed to however replace the thru hulls as a precaution so that theres peace of mind. The hull has now been pressure washed and is in great shape - hammer tested and structurally sound. It is getting a top coat of anti-fouling today. The zincs have all been replaced. The wiring is new as are the house batteries. The engine is in excellent condition and the oils have come back from the lab with green lights. I think the patch in the middle appears to have been a factory option for a sail drive - maybe a cosmetic project for next is to glass over that and fair it in. Despite the new engine and new North Sails, an important thing for me is that the marina is 3 minutes from where I live and has just six sailboats. The owner has been there for over 30 years and the moorage is grandfathered in and assumable. Buy the boat - get the slip!
Thanks once again for everyone who contributed to the discussion - I found it really useful to consider folks different opinions.
The background was that the owner was not able to attend to the boat during covid and the marina has quite a bit of stray current. He hadn't placed zincs on the prop shaft after its last haul out from 2 years ago (the sales photos on the Crescent Beach Marina web site). He was shocked to see the condition of the prop as anyone and has replaced it free of charge. The thru hulls I inspected inside and out and had a good poke around with a screw driver. There are some minor metal fragments that dislodge out of the side wall when poked from the underside but they are actually in reasonable condition as are all the seacocks - a tiny bit of green corrosion on the brass but the valves all turn with ease. The owner has agreed to however replace the thru hulls as a precaution so that theres peace of mind. The hull has now been pressure washed and is in great shape - hammer tested and structurally sound. It is getting a top coat of anti-fouling today. The zincs have all been replaced. The wiring is new as are the house batteries. The engine is in excellent condition and the oils have come back from the lab with green lights. I think the patch in the middle appears to have been a factory option for a sail drive - maybe a cosmetic project for next is to glass over that and fair it in. Despite the new engine and new North Sails, an important thing for me is that the marina is 3 minutes from where I live and has just six sailboats. The owner has been there for over 30 years and the moorage is grandfathered in and assumable. Buy the boat - get the slip!
Thanks once again for everyone who contributed to the discussion - I found it really useful to consider folks different opinions.
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Perhaps, if it was an option to build the boat with a sail drive or a shaft there was a depression built into the mold where the hole for a sail drive would have been cut out. I agree with whoever suggested that a filled in hole would have been faired more flush than that.
Oh boy, here we go again, playing it fast and loose while making it up as we go along.
A little outfit called the ABYC disagrees with you in their para. P-6 6.5.5.4 and says the clearance shall NOT exceed one shaft diameter.
Pretty much what I saw this morning in the yard :
No one said it the distance can't be larger than 1 shaft diameter. No one said there are not boats that have the props more than 1 shaft diameter away from strut, indeed, the prop on my boat is a little more (¼") than one shaft diameter. While ABYC standards do not carry the force of law, they are a compilation of best practices.Yeah, I'm making it up and you're the expert
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When prop shafts rotate the forces on the prop will cause the shaft wobble (probably not the correct technical term), i.e., the end of the shaft rather than rotating along its axis will begin to describe a circle. The longer the unsupported length of the shaft, the larger this circle will be. This makes the prop less efficient and induces more vibration, neither of which are desired characteristics in a powertrain.
After looking at a few photos of Mirage 27s I would speculate the boat was originally designed to use a sail drive and in later models the shaft and strut option was added along with diesel power. Because the hull sweeps up quickly, in order to use a standard drive train it was necessary to have a long strut and to extend the prop further aft to get the necessary clearance between the prop and the hull. During the repower of the boat in question, the installer added the block of something between the strut and hull and extended the prop further aft. The extra piece of something may also be necessary to reinforce the mounting because the hull is not thick enough to support the shaft. If this were a factory installed shaft and strut, I would have expected the builder to have laid up extra glass on the interior of the hull. I would also not expect to see the sail drive opening, it would have not been part of the mold or it would have been faired. This is of course, as I said, speculative, but the data fits the hypothesis.
As for me, I try to adhere to ABYC standards or as close to them as I can reasonably get.
Me ? I don't know nuttin'. I rely on the experts to tell me what to do.Right. I'm making it up and you're the expert
Hence ABYC P-6 6.5.5.4. Don't exceed one diameter clearance.
Yeah, I get it. Bottom line? Many production sailboats (and powerboats) are built with more (sometimes much more) than 1 shaft diameter between the hub and strut. Any contention to the contrary is simply ignorant.
I don't see that contention being made.
You specifically stated there is no standard... When in fact there is one.
Just because some boat builders don't follow that standard doesn't mean it isn't best practice or doesn't exist.
I just ran into that with hose choice. NMMA vs ABYC.. I will take the good fire and permeation rated ABYC hose thank you very much.
Do you really think it makes any difference with the tiny power output we have on our sailboat engines? My inboard ski boat had 260 HP driven with a 1" diameter shaft. I'm pretty sure it had the prop very close to the strut.
I don’t know the physics for sure, but I’m guessing the shaft RPMs and propeller hub mass have more impact than engine horsepower. I’ve read about some people having issues switching to Flex-o-fold props because the hubs are heavier and weighted further aft than fixed props.
I think it will have more to do with RPMs and prop weight than power. There are likely other variables, such as shaft diameter. Larger diameter shafts will be less subject to the wobble (or whatever the technical name is). Anyway, if the prop on your ski boat was close to the strut it was probably built to ABYC Standards or close to it.
We're in recovery. The boat is hauled. The leaves are turning. Soon snow will be flying. Spring is a long way off.Y’all are clearly bored