Trawler Forum

Trawler Forum (
-   Power Systems (
-   -   Matching Shaft & Prop Tapers (

Aquabelle 07-06-2017 08:16 PM

Matching Shaft & Prop Tapers
I have 2.25" stainless shafts with the SAE-standard 1:16 taper. I have been offered new props with the right diameter & pitch and bored for a 2.25" shaft BUT with a taper of 1:12 for some reason. I assume the two tapers must match....can the mis-match be fixed and if so, what is involved in doing this: or do I walk away?

Alabama Boater 07-06-2017 08:36 PM

Tapers must match. The 1:12 can be rebored to 1:16 as the small end is less diameter than what your shafts are. The key way will need to be broached to the 1:16 taper. You would need to find a good machine shop that has the proper equipment and fixtures. Cost in USA to do rebore would be in $250 or more each. Things can go wrong when machining, so for me, must start out at very good price.

Aquabelle 07-06-2017 09:09 PM

Thanks. I called an experienced machine shop and they told me the re-bore'd props would sit further forward on the shaft than my existing. Said it should be "no problem" to put a spacer between prop and prop nut. Any downside in doing this?

Alabama Boater 07-06-2017 09:37 PM

You should not need a spacer unless the length of the hub is shorter on the 1:12 props. The front of the hub @ 2.25" diameter would be in the same position as your current prop but if the hub is shorter the rear would be forward by the difference in hub length. If the set up is done correctly, the large end of the 2.25" bore has no material removed. That large diameter is used to center the boring setup. It should be able to center at 0.0005" total run out. I have heard of some shops using a taper reamer but I am not familiar with the set up used.

Aquabelle 07-06-2017 11:39 PM

Thanks again Al Boater...& I realize I mis-typed. The shop said the fwd point on the shaft would obviously remain the same as the hub's opening would remain at 2.25". But re-tapering the bore from 12 to 16 would shorten/narrow the hub (it is 5.75" now). However, I see what you all depends what my current props' hub thickness is...and since the boat is in the water I have no idea. Aquabelle is about to haul out for antifoul and I'm having the port shaft pulled to get a really good go at cleaning out a problematic traditional stuffing box (packing space larger on one side than the other, so some shaft misalignment I think. I'll replace the cutlass bearing at same time). I'll get the shaft checked for straightness and if as I suspect, there's corrosion at the stuffing box connection point, I'll get the shaft spray-welded/polished in that spot too. Anyway, while all that is going on I'll have the yard check that the shaft really is standard SAE 1:16 and they can measure the current props' hub thickness too. I won't rush to throw out my old manganese-bronze props just yet...but I might not send them off for reconditioning either, if all the measuring suggests the new ones might be a go with a re-bore. Around US$380 per prop here for changing taper to 16 plus costs of getting props to/from the shop. US$975 + transport for reconditioning of both existing props, so I'll keep that in my pocket for now.

Appreciate your input. Will update post & add a photo when hauled out in a couple weeks

Aquabelle 07-21-2017 10:21 PM

3 Attachment(s)
An interim update. I went ahead and bought the new Nibral props & they are in the shop having their bore tapers changed from 12 to 16. The shop suggested I also send them one of my existing props so they could get the taper even better matched to the shafts. Aquabelle was slipped Friday morning and the stb prop was taken off and sent to the prop shop as the very 1st job. The prop shop will also make bronze spacers to take up any difference in prop hub length between the re-tapered new and the old props, per posts #4 & 5 above. I left the port prop on to allow us to explore the shaft/stuffing box issues per post #5 with the prop weight bearing....and it soon became obvious that both the stern and the intermediate cutlass bearings are worn & need replacing....lots of slop in both. I am hoping this is the principal cause of the stuffing box problems (apart from the bad packing job done at last haul-out). Port prop was also then removed and we'll pull the shaft on Monday & inspect for corrosion at stuffing/bearing points; and straightness.

Attached is a pic of vessel up on slip; and another showing the PropSpeed on the props ( also on the shafts, though not in the photo) still un-fouled after 2 1/2 years & untouched by divers. Although the Australian members of TF are all PropSpeed converts, I know some of our US friends are sceptical...but take a look at the rudders (not a great photo I know...sorry, was a bit distracted). I normally get PropSpeed applied not just to props & shafts but to the rudders, skegs and bow thruster metals too. Last time I was hauled, at a different yard to my usual, I let them talk me into saving a few $$ by not applying PropSpeed to rudders & skegs. Instead they took back to bare, epoxied and applied a hard anti-foul (the hull always gets abalative). 4 months before the current haul-out, I had to get a diver to clean the un-PropSpeed'd running gear....and now, just 4 months later, all is severely foul'd with barnacles! The photo doesn't do the degree of foul'ing justice, but it is so extreme the yard is going to charge me a little more for the extra time in dealing with it.

I'll try to take better photos on Monday.

Aquabelle 07-24-2017 09:46 PM

4 Attachment(s)
Some progress and new learnings: the prop shop called me having examined the original props and compared to new, to say the old props sat well back on the shaft taper and that the new would be much further forward. Was I sure there was enough distance between original props and the aft skeg to accommodate this? I had the slipway guys measure up and reported a 48mm (~2”) gap available; happily the prop shop said this would be OK. The keyways of the original & new props were also different, so now as well as re-tapering to 16 & making up bronze spacers, they’ll also make up new keys. Props will be prop-scanned and balanced/matched also.
Meanwhile back at the slip, the team seemed to have no problems getting the Port shaft out….all 3.9m x 58mm (12.8’ x 2 ¼”) of it. As expected, pretty severe corrosion on the stuffing box end but good everywhere else. Photo below shows 200mm (7 3/4”) corroded section but only 45mm (1 ¾”) of this is within the packing area of the stuffing box; the balance made for an unattractive but harmless view between SB & trannie. This corrosion was obviously the explanation for the Port SB’s steady drip despite re-packing over the last 10 years; and the deterioration in the cutlass bearings since the last haul-out 2 ½ years ago must have exacerbated this by letting the shaft sit out-of-centre through the SB.
The shaft is double-tapered and so would usually have been reversible…but for some reason, the thread on the prop end is 1 ½” but only 1 ¼” at the trannie end. The yard kindly lent me their truck so with the prop shaft & coupling loaded, it was off for the 2-hour drive from Sydney’s eastern edge to an industrial area to the west, to meet up with a spray-welding outfit. When they saw my interest in the process, I was given a full tour of the facility. Pretty amazing, they spray-weld all kinds of coatings, not just the stainless I need: including hi-tech ceramics.
With the shaft removed, the worn cutlass bearings x2 were removed…and we found the ‘spares’ left on board by the previous owner 10 years ago didn’t fit! Also, there is a bearing behind the stuffing box itself in the stern tube and this had almost entirely disappeared. (The SB is bolted direct to the aft engine room bulkhead….no rubber hose….and right behind this is the stern tube with this newly-discovered bearing.) The slipway guys feel this bearing is redundant, as the shaft is supported by two bearings on the hull and by the SB itself…but since we’ve come this far, I told them to go ahead and replace the shaft tube bearing as well, so the SB operates just as a gland. I have to believe this will allow the SB to do as little work as possible.
The slipway team got the new anti-fouling done (but not PropSpeed). Now, while we wait for work on the props and the shaft to catch up, Aquabelle has been un-slipped and is sitting out on a mooring.

Insequent 07-24-2017 10:33 PM

Good progress! It sounds like the guys involved are all knowledgeable and pragmatic. Are you going to pull the other shaft and check it and the bearings as well? I look forward to you getting it all completed and reporting back on sea trials with the new props!

Aquabelle 07-24-2017 11:17 PM

Brian: Stbd SB has always run cool with zero drips and we try as we might, we couldn't get any wriggle between shaft & skeg bearings on Stb side I don't intend to disturb this. Will re-check Stb bearings at next haul-out in 2 1/2 years: at least now I know what to look for and what's involved/required to address (and who to go for: amazingly I've only been able to find the one spray-welding shop in Sydney and the various marina guys I called around to prior didn't even know of this one !) I did mean to ask about your original (still current?) SB's...are they like mine, bolted direct to aft bulkhead...or did/do they have flexible rubber hose components?

BruceK 07-24-2017 11:44 PM

Aquabelle, what prop & shaft shop you are using? I understood Porters were the go to experts, it sounds like you found someone else.

Insequent 07-24-2017 11:56 PM

1 Attachment(s)
No rubber components on mine. They mount onto a block glassed between stringers.

Aquabelle 07-25-2017 12:57 AM


Originally Posted by BruceK (Post 576401)
Aquabelle, what prop & shaft shop you are using? I understood Porters were the go to experts, it sounds like you found someone else.

Hi Bruce: I bought the props from a shop in Brisbane and sent them direct to Porters here in Sydney for the re-tapering & associated work. The shaft was pulled out by Newport Marine Services (NMS: at Royal Motor Yacht Club at Newport on Pittwater) and is with Flame Coatings for spray-welding of the corrosion. The shaft will come straight back from them to NMS...nothing for Porters to do with that, as I also sent an original prop into Porters so they could work off that, not the shaft.

Aquabelle 07-25-2017 01:02 AM

Brian: that is EXACTLY the SB I have too...but where you have a block between stringers, I have the full aft engine room bulkhead. I'm now willing to bet that if you removed your shaft and in-bolted that SB from the block, you would see looking into the 'glass tube visible behind that block, another rubber bearing. Unless there is something behind the block, I'd say the only access to that rubber bearing is by 1st removing the SB, as I am doing on Thursday a.m.. Do you have a photo looking the other way, from behind the block the SB is mounted to....or do you recall if the glass tube just mates up to the back of that block with no fittings, etc?

Insequent 07-25-2017 01:10 AM

The glass tube just mates to the block. There are no fittings of any kind aft of the block in the pic. No idea whether I have the rubber bearing you refer to. During my refit I had new shafts and bearings installed, but it must have been done during one of my visits back to Brisbane. I don't know if the SB was unbolted at the time. I can't recall seeing the SB without a shaft in it either.

Aquabelle 07-25-2017 04:55 AM

Brian: you can't see the bearing in that tube unless the shaft is out AND the compression plate & the packing are removed. The bearing seems to fit inside a bronze tube; I am not sure whether this is bolted to or is even an integral part of the SB itself. I'll know more when my SB is actually unbolted & removed. I'm hoping an experienced TF member has come across this setup before & will comment. I don't think this belt-&-braces approach is used on contemporary recreational vessels; it may have been an Ed Monk Snr special.

Insequent 07-25-2017 05:12 AM

I will be interested to see what you discover. I'm sure the OA yard built our boats almost identical. Other than yours being one of the handful of flushdeck configurations.

By the way, I believe it was Ed Monk Jnr that was responsible for the Mark I design. Of course he may may well have taken inspiration from his father, or Art DeFever, or others who produced the 'classic' raised pilothouse design as well.

What I don't know is how much Ed was involved in the detail, such as the SB we are talking about. There may well have been others responsible for this area, or a 'standard' Taiwanese approach to things like this. But I do believe there was a commitment to quality and good design. They were built at a time when knowledge was rapidly evolving, and yes, when Fleming came along a few years later they were built a little better. Indeed part of the demise of the Mark I was that they were expensive to build. Hence the Mark II. Cheaper to build, a nice boat for sure but I don't think it has ever had the enduring appeal of the Mark I. Hats off to both Ed Monk and Ocean Alexander for both!

Aquabelle 07-25-2017 06:59 AM

Quite right was Ed Monk, Jr. Here's a link to a recently re-launched OA site. You will see my motor yacht model pictured....3rd photo down on left side. Heritage - Ocean Alexander The 3rd partner, with Ed Monk & Alex Chueh, was an Australian...a Gold Coast-based yacht broker, so we have a connection of sorts there too! I have an electrical wiring diagram original to my boat, hand-lettered and signed by Alex Chueh.

Paul g

Aquabelle 07-25-2017 06:04 PM

1 Attachment(s)
Brian: I THINK I now know what to expect when the SB is unbolted and removed. I reckon it will be like the big heavy Model 102LB shown on the attachment to this post. It incorporates a "1/3-length standard rubber sleeve bearing" right behind the packing rings. The attachment shows a modern Duramax model, but in the early-to-mid '80's companies like Buck Algonquin and Wilcox Crittenden were making this sort of SB too. Of course ours may have been cast in Taiwan....I have found a few bronze fittings that have Chinese characters on their in-finished undersides so the yard must have made these or had them made locally...perhaps the SB's were the same. I imagine they would have been high-cost items to bring in from the States.

Insequent 07-25-2017 06:58 PM

I don't think I had any rubber, based on my refit invoices. All I could find was 6 x bearings. They were 2" x 2 5/8" x 8" in size.

Your set-up is a little different in that shaft size is larger. But was that original, or a mod when your PO installed the larger engines?

Aquabelle 07-26-2017 01:14 AM

Brian: 6 bearings is 3 per side. One for the big skeg against the prop; one for the intermediate bearing; and the 3rd.....for the stuffing box?? Maritime archaeology begins tomorrow...

I don't know if the shaft was replaced with the engines. I do know the skeg and intermediate bearing holders have plenty of room to take different thickness cutlass bearings. The new ones (naval brass shells) for the two skegs have to be shimmed down a little to fit, but these things come in different outer wall thicknesses (while remaining constant for shaft of) for just that purpose apparently.

All times are GMT -5. The time now is 12:54 PM.

Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012