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| Author: | Cruisin Home [ Tue Aug 02, 2011 9:43 am ] |
| Post subject: | 348 Vista speed vs rpm |
I ahve 2006 348 Vista with Gas 5.7liter Volvo Penta. Not sure of my prop size/pitch but had "tuned" last year after striking a log in river. I am little concerned that I am not getting the right speed vs. rpm: at 3000 rpm usually around 10-12kts at 3800 rpm get approx 20 kts this is usually with full load of fuel/water and fairly calm seas with trim tabs fully extended. I dont like to run it above 4000rpm. does anyone else run higher? Is this normal speed vs. rpm? What does everybody else get? |
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| Author: | jsimon [ Tue Aug 02, 2011 10:24 am ] |
| Post subject: | Re: 348 Vista speed vs rpm |
This should help http://www.fourwinns.com/past_product/specs//2006/30%20348%20Vista%20(p98-101).pdf |
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| Author: | Cruisin Home [ Tue Aug 02, 2011 11:43 am ] |
| Post subject: | Re: 348 Vista speed vs rpm |
Thanks jeff. but seems like I dont get close to those numbers. Will check my prop. Others? |
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| Author: | jsimon [ Tue Aug 02, 2011 11:50 am ] |
| Post subject: | Re: 348 Vista speed vs rpm |
If your trim tabs are fully extended, I take that to mean down, then you are unnaturally pushing the bow of the boat in the water. That will make a huge difference. You should have the tabs fully up, and properly trimmed out on the out drives. Once you are on plane and cruising use just as a little of trim tab as possible to level the boat from side to side. |
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| Author: | Cruisin Home [ Tue Aug 02, 2011 12:00 pm ] |
| Post subject: | Re: 348 Vista speed vs rpm |
I have straight shafts not outdrives. But maybe i will play with trim settings. |
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| Author: | Cruisin Home [ Tue Aug 02, 2011 12:03 pm ] |
| Post subject: | Re: 348 Vista speed vs rpm |
checked my survey and it says I have the 18x24 4-blade prop. On the FW datasheet shows that prop to be about 20% slower than the F4. I still am running below that. Maybe the admiral has more stuff on board than I thought! |
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| Author: | jrcinnh [ Tue Aug 02, 2011 1:49 pm ] |
| Post subject: | Re: 348 Vista speed vs rpm |
Don't forget the F4 is a prop set for the dual prop Volvo penta outdrive. I have the 320 HP Volvo outdrive and get numbers like the chart. I can routinely get WOT speeds over 41 MPG. I usually cruise around 3700 RPM and 35 MPH. I think the inboard numbers posted there are a little generous. Bill has the 6.0 liter, so maybe he will chime in. Also be carefull switching between knots and MPH. Even with all this, I still think you are not getting the perfromance you should. So what can contribute? Others mentioned tabs, general rule is the tabs all the way up (press "Bow Up" for 20 seconds) will give you the best speed. So tabs all the way down until up on plane and then tabs all the way up. Bill suggests and I concur, that a small amount of down tab will provide a more stable ride especially in mixed seas. But for maximum speed in dead flat seas, use full up tabs. Other things to look for are overloading and a dirty bottom. |
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| Author: | Cruisin Home [ Tue Aug 02, 2011 2:10 pm ] |
| Post subject: | Re: 348 Vista speed vs rpm |
Listed Speed 18 x 24 prop mph knots mph knots 2000 11 9.5 9.0 7.8 2500 16 13.8 13.1 11.3 3000 23 19.8 18.9 16.2 3500 28 24.1 23.0 19.7 4000 32 27.5 26.2 22.6 4500 34 29.2 27.9 24.0 WOT 36 31.0 29.5 25.4 If I read the table right for a Twin 5.7Gxi 320 inboard the speed is the left table above. If I reduce by 18% for the prop I have I get the numbers in the above right table. They are somewhat close to the numbers I am getting on-plane. perhaps with a little up trim I will get more. but probably am little overweight (admiral), and our bottom gets slimed up her in the merrimack river. I use the apply every year ablative coating which is a bit less smooth than the epoxy versions. |
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| Author: | Cruisin Home [ Tue Aug 02, 2011 2:12 pm ] |
| Post subject: | Re: 348 Vista speed vs rpm |
wow that table posted kinda lousy. rarely get a very flat calm surface conditon here as well, so likely loose a little due to sea condition. I am sure they tested these numbers on "glass". |
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| Author: | wkearney99 [ Tue Aug 02, 2011 6:10 pm ] |
| Post subject: | Re: 348 Vista speed vs rpm |
Mine's been running a bit slow lately. I think my throttles need adjusting as I'm not able to make 5k rpms, tops out at around 4200. We typically run at about 25mph at 3500rpm. And I measure the speed using the chartplotter SOG (speed over ground). Which can be different than STW (speed through water) especially when going against a current. As in, your SOG might read 20mph, but if you're heading in to a 4mph current you're actually doing 24mph STW. Reverse is true running with a current. But there's generally not enough of a current on the Bay to have it factor into speed calculations. I've never gotten 38 at WOT. Maybe 35, tops. I usually have to give it a lot of tabs, otherwise it tends to run too high at the bow. |
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| Author: | jrcinnh [ Tue Aug 02, 2011 6:49 pm ] |
| Post subject: | Re: 348 Vista speed vs rpm |
[quote="Cruisin Home"]....but probably am little overweight (admiral).... you may want to rephrase in case she reads this |
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| Author: | Cruisin Home [ Wed Aug 03, 2011 8:05 am ] |
| Post subject: | Re: 348 Vista speed vs rpm |
hahaha definitely the boat overweight because of what she brings onboard. Not her! yeah, definitely not getting as good as you Bill, prob the weight, slimy bottom, and needing a bit more trim in these seas up north. maybe I am stern heavy, had a thought to see if I can shift some of the stored weight to bow, might make a diff. but I swear I was getting a few more mph before I had props tuned. cost a pretty penny and supposed to give you more speed. maybe I will check when i pull out this year. |
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