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Author Topic: Dead Reckoning and Basic Piloting
 jbartra posted January 28, 2020 06:34 PM                   Hello,I came a across a problem and I would like your help if possible. I have sent an email with screen shots and my calculations to the classroom.I spent a few hours on this problem and I would really appreciate your help.ThanksJorge
 David Burch posted January 28, 2020 07:50 PM                   glad to help, but you need to post the question here along with any needed images.I want to stress however that the problem we are looking at here is not from any Starpath materials, but rather one you have run across from another source. From: Starpath, Seattle, WA
 jbartra posted January 28, 2020 10:08 PM                   Hello David and thank you for the help!!!!! I need your advise on question 6 and 9 from this USCG test. Please see below the details. For this problem I am using the 1210 Tr chart in OpenCPNGuidelines for this problem:Lines of Position. A bearing taken on an object can be plotted as a line of position (LOP). In order to use the LOP for navigation the object must be charted. LOPs can be established using bearings from the steering compass, from a hand bearing compass, from a pelorus, or from radar. If the steering compass is used, deviation is a factor which must be considered in converting the bearing to True. It also will almost always require turning the vessel in the direction of the object and sighting across the lubber line. This is because the steering compass on most small vessels is located where it cannot be sighted across except from astern looking forward. This is the least desirable method of determining a LOP because it means turning the vessel off course. Further, it would be very difficult to establish a second LOP, for a fix, from the exact spot or at the same time. When using the hand bearing compass, deviation is ignored. This is because the hand bearing compass can be used from anywhere on the vessel and using the compass in the same place every time would be virtually impossible. The vessel’s magnetic field would affect the compass differently each time it was used. Since deviation is the result of the interaction of the vessel’s magnetic field with the Earth’s magnetic field on the compass, its consideration is impractical. LOPs from hand bearing compasses are treated as magnetic bearings, to which only variation is applied to determine the true bearing. A hand-held fluxgate compass will eliminate the problem of deviation. Variation is 15 W in the area.Here is the problem:On 5 April you intend to depart your marina in New Bedford for Dutch Island Harbor, Conanicut Island. After conducting some personal business you will head for Tarpaulin Cove in Vineyard Sound where you plan to anchor for the night. Your vessel is a 46 ft twin engine trawler yacht, the Helena, call sign: Coast Guard Auxiliary Vessel 46143.Daylight Savings Time is in effect. You plan to pass under the Acushnet River Bridge (between the two islands) at sunrise, 5 April. You want to follow the indicated channel to green buoy “11”, marked by a green light flashing at four second intervals. Upon reaching G “11” you intend to leave the channel and head south direct to R “8”Fl R 4sec GONG. You would like to hold your speed to 5 kts while in the narrow channel to G “11”.You are equipped with radar, LORAN, a high-quality hand-bearing compass, and you have a pelorus to determine relative bearings. Variation for the whole area of the cruise is 15°00' W.1. What time is sunrise in New Bedford?a. 0653b. 0521c. 0619 Correct Answerd. 05532. What is the height of the tide at sunrise?a. 2.9 ft Correct Answerb. 1.0 ftc. 4.3 ftd. -0.4 ft3. You find you cannot hold speed to 5 kts using both engines so you opt for asynchronized 1600 rpm power setting. This results in a speed of:a. 5.7 ktsb. 6.0 kts Correct Answerc. 6.4 ktsd. 5.4 kts4. You pass under the bridge behind schedule at 0700 at a steady speed of 6.0 kts.What is your 0730 dead reckoning position and what is your ETA at G “11”?a. 40° 35.7' N, 70° 53.3' W, 0733b. 41° 35.7' N, 70° 53.3' W, 0733 - Correct Answerc. 40° 35.7' N, 71° 53.3' W, 0731d. 40° 35.7' N, 71° 53.3' W, 07355. You depart G “11” at 0735 with both throttles set to 1950 rpm. What is your speed?a. 7.4 ktsb. 9.0 kts - Correct Answerc. 7.7 ktsd. 8.7 kts6. What compass course do you steer for R “8”?a. 188°b. 198°c. 158°d. 210° I don’t understand how the Course is 210 T. I am using 197° M + 15 W Variation I get 212°T – Unless my assumption of the starting point near to G “11” in my chart is wrong. Please see below my LOP. I have done this in paper chart and Opencpn but still don’t get the correct answer.(please see screen shots 6A)7. At 9 kts, how far is your 0800 DR position from G “11” and where is it?a. 3.75 M, 40° 31.7' N, 70° 53.4' Wb. 4.50 M, 40° 31.0' N, 70° 53.4' Wc. 4.50 M, 41° 31.0' N, 70° 53.4' Wd. 3.75 M, 41° 31.6' N, 70° 53.4' W - Correct8. What is your ETA at R “8”?a. 0813b. 0818 - Correctc. 0823d. 08289. At 0759 you take a bearing on the tower on West Island, reading 054° directly offyour hand-bearing compass. What is your estimated position?a. 41° 32.1' N, 70° 53.5' Wb. 40° 31.6' N, 70° 53.0' Wc. 41° 31.8' N, 70° 52.8' Wd. 41° 31.6' N, 70° 53.0' W I am confused here because I think I cannot figure out the answer on question #6 but independent of the course in question #6, if I do the hand-bearing compass = 54° it should be based on the magnetic course right? So that’s what I did but I am off by 0.28 nm based on the text’s answer. Any help would be greatly appreciated. Screen shots in the next post (9A)
 jbartra posted January 28, 2020 10:09 PM                   screen shots for question 6
 jbartra posted January 28, 2020 10:17 PM                   screen shot for question 6. Sorry I keep getting error due to the wrong format
 jbartra posted January 28, 2020 10:20 PM                   screen shot for question # 9
 Capt Steve Miller posted January 30, 2020 07:50 AM                   First on #6 you indicate that you used 197°M + 15°W to get 212°T. Going from M to T you Subtract Westerly Variation, thus the True is i82°. The Compass Rose on the chart would show that as well.Second, for #9 I got an estimated position of 41° 31.5' N, 70° 53.4' W for 0759 by working this problem on a paper chart. This position is based on the assumption that we are on our proposed course line between G "11" and R "8".I hope that this helps. From: Starpath
 jbartra posted February 01, 2020 09:28 PM                   Hi David,Yes it helps. I think I will not use this manual. It is has several typos. I will use your book and exercises to get ready. I passed Exam A, I just need to pass Exam B which is all Charting.Thanks !!Jorge
 David Burch posted February 01, 2020 09:32 PM                   OK. we have a 1210TR workbook at this linkhttps://www.starpath.com/catalog/books/1979.htm From: Starpath, Seattle, WA
 jbartra posted February 03, 2020 07:37 PM                   perfect!!! thank you Sir!! I will buy it...
 jbartra posted February 03, 2020 07:44 PM                   Hi David,Do you offer an e-book version? I ordered it but it only comes as printed book?Let me know pleaseJorge
 David Burch posted February 04, 2020 07:35 AM                   Yes. we have it. Our ebooks in various formats are listed here: https://www.starpath.com/ebooks/starpath_ebooks.html From: Starpath, Seattle, WA
 jbartra posted February 04, 2020 11:25 AM                   thank you Sir, just placed the order!!

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