Motor height for best performance

[northshoremb]

I had to rebuild my transom on my 14'r Sea Nymph 1973. I was reading on here and other places that the fine (plate) pretty much where the lower end meets the top end should be level with bottom of boat for best results. Anyways I rebuilt the transom to that requirement and boat seems to gurgle when doing a turn even at a 10 degree turn. Also there was a website on here that calculated the weight of boat model and weight in the boat, prop pitch and motor which said it should do 23-25mph with my 1980 Evinrude 15hp 9.5x10 prop. On GPS I only get 27km an hour wide open and had her tuned up at the boat dealership 2 weeks ago.

What Im wondering is it cause Im either to high or to low on the transom?? Here are some pictures of how she sits.
http://i570.photobucket.com/albums/ss143/northshoremb/IMGP7210.jpg
http://i570.photobucket.com/albums/ss143/northshoremb/IMGP7209.jpg

 

[hwsiii]

Re: Motor height for best performance

Mb, I am not exactly sure what you are talking about when you say gurgle. If the motor is too high for the prop you will experience ventilation (RPM go up and you can feel the prop slipping and the motor rising in speed). But from looking at your setup on the boat it appears you are still too low on the transom, although it is hard to tell from pictures. When the lower unit sits tool low in the water you experience a lot of drag which slows the boat down, and limits the RPM.
If you don't have a tach you can buy a Tiny Tach for about $ 50 and between the tach and the GPS speed we can make sure you have a very good prop for the boat.


H

 

[northshoremb]

Re: Motor height for best performance

when I look from the side it looks to be even with the bottom keel. I even rebuilt transom 2" higher then the transom my grandfather had on there. Have no recolection of how it ran at that height since that was 15 years ago. All I know is it sounds like its running smooth except when I turn it feels like it is starting to slip and makes more noise. I have no idea what the RPMs are but from reading lots of threads on 14' boats with 9.9s hitting 25mph it makes me wonder WTF is wrong with my 15hp when it can only hit 15mph

Maybe the throttle isn't twisting fully open for some reason?? It there a sight on the web thats shows how to check for this for a 1980 15hp Evinrude??

 

[hwsiii]

Re: Motor height for best performance

Mb, fill this out for me and let me run some numbers on my program.
Iboats Boat and Motor Info
1. Year, make and model of boat
2. Length, width and base weight of boat, look for boat decal on back of boat
2a.What is the recommended HP for your boat
3. Number of people and gallons of gas normally on boat
4. What do you use the boat for
5. Is it a Deep Vee and if so how many degrees of deadrise
6. Year, make and model of motor
7. HP and gear ratio of motor IMPORTANT
7A If you have a mercruiser and don?t know the ratio get your serial off the outdrive and go here http://www.sterndrives.com/mercruisersterndrives.html
8. Manufacturer?s recommended Wide Open Throttle (WOT) range
9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches
10. Is it a bass boat or does it have a pad bottom
11. Does it have a hydrafoil, dolefin or trim tabs
12. Make, model, diameter, pitch and whether SS or aluminum prop
13. WOT RPM and speed from your current prop and how much gas and how many people were in the boat for the test data and is the speed by GPS. If you do not have a tach you can buy a Tiny Tach for $ 50
14. Are you at sea level or a higher elevation, give us the elevation in feet
15. Has your motor been tuned up lately and have you checked that the carburetor butterfly is opening all the way, checked compression, and looked at the plugs and checked spark, all of the forgoing could be the reason your prop is not attaining full RPM
16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop
17. Does the prop show any damage that you can see
18. What problems are you trying to cure or what are you looking for the boat to do that it is not doing the way you think it should or to your expectations

REMEMBER, The numbers I give you will be NO better than the information you give me

The only thing I ask of you is to come back and give me a report of WOT RPM and speed for my database.

H