I would skip the 20km swim.

You should be OK. I'm not sure about transferable fitness. I'm a similar pace to you 27/28 70.3. If I don't swim, I lose swim fitness and speed. Doesn't matter how much I run/ride. I don't think trying to swim 25km a week is a good idea and that recommendation is pretty arbitrary. You have swimmers of all sorts of abilities, some could do it on 5km/week.

Personally I would swim 3 times a week, try and push those sessions out to 4km. The cut-offs are very generous and you're a good enough swimmer to get by with lower volume, even if the conditions are shit. I did the 10km Rotto qualifier a few years ago. It was cancelled because of bad weather and they moved it to boxing day! So I did it with a raging hangover and my so-called support crew failed to get out of bed (also hungover) so I did the 10km sans any form of fluids or nutrition. I think my time was 3 hours and it was fine. And that was just with 70.3 training, 2 - 3 swims a week. I didn't end up doing Rotto as I got a shoulder injury and now Ironman gets in the way. But I would have no problem doing Rotto on limited volume. That said, my mate trained his arse off for it a few years ago, got quick in the pool, consistent laps at 1.20/100m and he had a hard time. The conditions were crap. He still easily made the cut offs. But he did like 7hours instead of 4 something.

Not sure whats best but I swim 18-22km/week during an IM build. I am a 1hr swimmer and looking to knock some time off that and expect to continue that trend into IM St.G.

Probably selling yourself a bit short on the swim ability there. With that being said, I would say that if you have a swim background (swam as a kid), which given your times you might have, but then I would say it can be less of focus. Given you are already at the front of the race with your swim it maybe more beneficial to spend less time on swim prep. If you weren't as good of a swimmer my answer would be different. And with all that being said, swimming can be a great way to work on aerobic fitness and anaerobic systems with less injury risk than say running. But if you like to swim, I say do it!

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This is a pretty tricky situation and I think will really depend on which of these events is your real priority.
For the Rottnest swim there are a few things to take into consideration. Most of the squads here in Perth that prep specifically for that event swim about 4 times per week with one of these sessions being between 2-3 hours (longer closer to the event). So the overall swim time/volume is not too bad in the scheme of things. However, I have found that IM training has really impacted on my fatigue levels when it comes to swimming so the two do not go really well together. I find the running in particular tends to leave me pretty battered for the pool, I can still get through the work but just not feeling as sharp as I would normally.

The Rottnest swim can also be a relatively cold open water swim, not as bad as the English Channel but still such that "lean" swimmers can suffer from hypothermia pretty easily (I had a friend record a sub 32 degree temp at the end of his solo, he does not remember the last 2 km). But adding some fat to your frame is not great with an IM just around the corner.

Added to all of this is the uncertainty re weather for the Rottnest swim. One reason I am reluctant to do a solo is that I don't want to concentrate on swim training for four months only to find the race cancelled on the day due to weather (which admittedly has not happened that often to date).

So, putting it all together...I think on balance the swim is going to need to be your main focus as you really can't wing your way through a tough 20 k open water solo swim like that. Keep the bike fitness up but may need to drop some run fitness to maintain the swimming load....lower the expectations for IMNZ.

Just my 2 cents...!!

In a simple way it's too much swimming when the time spent on either bike or run would improve your overall performance. You'd possibly be fine with a long swim of 4-5km, a faster swim 2km main set and maybe an easier technique/recovery session, but you could skip this one.

So for Ironman, if your already a strong/fast swimmer, it would be safe to put swimming in to maintainence and use the extra time to ride.

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Delay Rottnest by a year, max out at ~12k per week in the pool, put the balance into riding, running & recovery.

You swim so fast, I am at about 14 - 18 km / week in swim training yet my speed is about 81 minutes for 3.8 km. I'm not actively training for a triathlon and I'm now dedicated for training a 14 km marathon swimming race. Am I doing junk miles that it will be better for me to cut back my training at my current slow speed?

If the IM is your primary goal I would still do both but not swim 20-25k every week. You’ll be fine doing a couple bigger weeks in the 35k range but you can use those as off weeks from biking and running. 35K split between 3 swims is only 3 sessions of 3 hours which isn’t really that bad. Still gives plenty of bike/run or rest time. Do that for a few weeks leading into the swim and you’re golden. Keep in mind a lot of people on here take 15 hours to do what you can swim in well under 10, and your training volume is already very high by AG standards so a 9 hour swim week isn’t even cracking 50% volume for you.

FWIW I’ve done well on swims in the 16k range with only average swimming volume a couple long days a week, and had plenty of time to train other disciplines.

You pose an interesting question - I had the same discussion with my coach this year and we decided to up my swim volume from 3 practices per week @ about 15k/week to 4 practices @ about 20k per week with no other changes in bike/run training. For reference, I am a 51-53 min IM swimmer and was a lifeline distance swimmer growing up.

The extra 5k/week definitely helped my swim fitness. It didn't necessarily make me faster out of the water, but I did make the swim leg easier and help me start the bike fresher. But I had to sacrifice some rest to do this - I struggled a bit more through the rest of the week on balance. Everything comes at a price.

For you, I would weigh whether or not you can still get the rest you need if you do up your swim volume. 20k+ per week is definitely beneficial but it requires a lot of time, and you have a 9-5 job. I would say try it out and see how you feel and go from there.

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Strava

The swim is my favorite event and I like to do open water swims too. I swam club and in college the 1,650yds was my best event. For me swimming ties everything together. I think you have to ask yourself what are your goals. For me I have found out the amount of time and yardage that works for me and allows me to achieve my goals. I think what other posters are implying is that adding additional meters might provide you only diminishing returns in terms of time improvement for the additional time investment.

I swim a work out of about 1-1.5 hours 5 times a week, which is about 13-15K (not including warm up or warm down) My total volume changes through out the season, and the structure of the workout changes too. For example a the beginning of the season I will focus almost exclusively on doing drills.

Good luck

A 20km swim shortly before an IM isn't the best idea. The training isn't complimentary.

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If you are determined to do both races, just know that one or both suffer a bit from being so close together, but you are not winning either, so what then? 20 hours a week is a lot of time to train, so there is no need for anything to suffer as you and others have put it. If it were me, I would swim 4 or 5 sessions a week of an hour, or 75 minutes if just 4 times. That should get you to just above 18k a week, and leave 15 hours to bike and run, which is what a lot of people have for all 3 sports.

Of course there is some crossover training affects, both ways too. But mostly it will cross over to your ironman. Maybe 3 weeks out from the swim race, do one week of 25k swimming, but that should be it, then taper off the yardage all the way to the ironman. The week after your big swim, you can mostly do bike and run blocks, with maybe two one hour swims in there. You will have to back off all intensities the week before your swim, and of course the few days after. Then you will have maybe 5 to 7 days in there for some good work outs, but mostly just staying healthy and uninjured.

It can be done, you have a lot of training hours, but the real point is that you will have to recover from those 20 hour weeks for it to be effective. The swim will be off by maybe 5% of what an all out effort would have been, and the Ironman maybe just a couple %, so the difference of having a good day, or a really good day..Go for it, just dont get all worried about either so much, as long as you get your work in..

Hi everyone

Thank you so much for the answers and the sound pieces of advice. Reading all this, I feel like getting the fitness level to race a 20km open water swim while training for an IM is not necessarily an issue.

However, the main problem with the Rottnest island swim may be the uncertain conditions…(high risk of hypothermia and I am a “lean” guy not planning on putting on weight). I will try to maintain 15km/week swim volume and see how I go with the rest of the Ironman training to make a decision early next year.

Thank you

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It doesn't get easier, you just get slower
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I second what Monty said.

This is how I would break it down

1. Swim+ run focus weeks = 10 hrs swimming, 4 hrs bike intensity focus, 6 hrs run
2. Bike Focus weeks = 5 hrs swim, 12 hrs bike, 3 hrs run

Rinse, repeat

You will lose zero on your bike + run prep and will be aerobically stronger due to a high swim volume. In your IM you'll get to T1 without even burning a single match and all that time in the pool will help your TT bike fitness. Alterating low volume and high volume run weeks and low volume and high volume swim weeks will help with injury prevention in both sports.

My only "worry" would be that your 20km swim race you're going to be doing at a low intensity. I don't know if it is 20km no wetsuit or with a wetsuit. I did a 12km lake crossing swim in 21C water this year and almost all my friends who raced no wetsuit got hypothermic just because of the time in the water and the low intensity...at some point if you are a 61 kilo athlete, you're not generating enough body heat due to the low swim intensity and whatever heat you generate is being sucked out of your body just because you'll be in the water for 6 hrs or so.

2 weeks after your 20km swim race is plenty of time to recover for an IM for a 20 hrs per week athlete.

Rottnest channel is non-wetsuit only race (I have a few friends doing that, but I'm not doing because I have no interest in Australia). However, are you exaggerating that all your friends got hypothermic for a 12 km lake crossing in 21°C? I did a 13 km lake crossing this July in 22°C and it was a bit warm for me (I was 67 kilo at that time), and I did the race at a relative low intensity as I didn't have enough high intensity training beforehand to sustain 13 km at race speed. I'm not a good swimmer though, my 3.8 km time is now 81 minutes.

I'm now training for intensity because I'm planning to do another marathon swimming race of about the same distance, but with lower water temperature (18°C expected).